Recruiting T cells in cancer immunotherapy

Recruiting T cells in cancer immunotherapy

  • April 8, 2021

Immunotherapies that enhance the ability of the immune system to target cancer cells have proven effective in a variety of tumor types, yet clinical responses vary across patients and cancers. The most effective immunotherapies to date are immune checkpoint blocking antibodies, which target inhibitory surface receptors expressed by T cells, particularly programmed cell death 1 (PD-1). One of the few robust correlates of clinical response to PD-1 blockade is the presence of tumor-infiltrating T lymphocytes (TILs) prior to treatment, with immune-infiltrated tumors achieving better responses than “immunedesert” tumors (1). Therefore, it has been widely assumed that PD-1 blockade reinvigorates preexisting cells within the tumor microenvironment (TME). However, recent studies of T cell dynamics suggest that the T cell response to immune checkpoint blockade (ICB) may originate outside the tumor and rely on peripheral T cell recruitment. This has important implications for patient selection, predictive biomarkers, and design of combination treatment regimens.

The site of ICB activity has historically been predicted from the expression pattern of the target inhibitory receptor and its ligand. The first immune checkpoint inhibitor that was approved for cancer targeted the cytotoxic T lymphocyte-associated protein 4 (CTLA-4) receptor, which is primarily expressed by CD4+ effector T cells and regulatory T cells (Tregs). Given that the CTLA-4 ligand, B7, is not expressed on malignant cells but rather on antigen-presenting cells (APCs) in the lymph node, CTLA-4 blockade was predicted to act on a lymph node–resident population of CD4+ T cells, which is subsequently recruited to the tumor. Indeed, studies in mouse models and patients have demonstrated that CTLA-4 blockade induces expansion of a subset of tumor-infiltrating CD4+ T cells expressing inducible T cell costimulator (ICOS), and increased ICOS+CD4+ T cell frequency following CTLA-4 blockade correlates with clinical response (2). Given its expression, CTLA-4 blockade has also been hypothesized to deplete intratumoral Tregs; however, this has not been consistently observed in patients (2).

Several monoclonal antibodies targeting PD-1 have since been approved for the treatment of multiple cancer types. PD-1 is expressed by several subsets of activated CD8+ and CD4+ T cells and is highly expressed on exhausted CD8+ T cells that show diminished cytotoxic responses to antigens (2, 3). Moreover, the ligand for PD-1, PD-L1, is expressed by malignant cells as well as APCs, and high PD-L1 expression within the tumor can correlate with clinical efficacy (1). These data suggest that in contrast to CTLA-4 blockade, PD-1 blockade may act primarily on tumor-resident T cells. The reinvigoration of T cells in the TME, particularly exhausted T cells, was further supported by studies in mouse models of cancer and chronic viral infection, which demonstrated that PD-1 blockade could induce proliferation and effector properties in chronically stimulated T cells (3).

However, it has been difficult to reconcile this singular paradigm of PD-1 action on tumor-resident T cells with observations that suggest a systemic immune response. For example, T cell proliferation and activation are prevalent within the tumor-draining lymph node (TDLN) and peripheral blood following PD-1 blockade in mouse tumor models (4). PD-L1 blockade within the TDLN promotes tumor rejection similar to that induced by systemic therapy, and the inhibition of T cell migration prior to PD-1 blockade abrogates tumor rejection, suggesting that the TDLN may act as a reservoir of PD-1 and PD-L1 blockade–responsive, tumor-reactive T cells (4, 5). Moreover, tumor regression following PD-1 blockade in mouse models is dependent on interactions between APC-derived B7 and the T cell costimulatory receptor CD28, which occur in the lymph node (3). In particular, recent studies highlighted the importance of PD-L1 expression on classical dendritic cells (cDCs), suggesting that PD-1 blockade may act at the level of cDC-dependent T cell priming and activation (5, 6). Further profiling of human T cell responses to PD-1 blockade in melanoma patients revealed increased T cell proliferation in the peripheral blood compared with the TME, suggesting that T cells may be activated peripherally and then recruited to the tumor (7).

A systemic antitumor immune response to PD-1 blockade is further supported by synchronous regression of multiple metastatic lesions after treatment (8). Similar to the abscopal effect, which is characterized by distant responses to site-specific tumor radiotherapy (9), uniform patterns of response among individual metastases suggest that peripheral immune cells may play an important role in the clinical response to ICB (8). Genomic profiling has also demonstrated that T cell exhaustion is epigenetically fixed, suggesting that PD-1 blockade may be unable to rescue exhausted TILs (3).

A productive immune response following ICB results in the clonal expansion of tumor-specific T cells, which can be tracked across different tissues and time points by profiling T cell receptor (TCR) sequences. TCR sequencing allows for preexisting T cell clones to be distinguished from newly activated T cells recruited from distant tissues. Early efforts to profile TCR dynamics in patients receiving anti-CTLA-4 therapy revealed a broadening of the peripheral T cell tumor-reactive TCR repertoire, supporting the idea that CTLA-4 blockade may lower the threshold of the strength of TCR signaling that is required for activation (2).

Tracking of peripheral T cell clones using TCR sequencing before and after ICB demonstrated that melanoma patients with a clinical response to therapy have significantly more clonal expansion and T cell turnover following therapy compared with nonresponders (10, 11). However, whether peripherally activated T cells traffic to the tumor remained unclear. Profiling of phenotypic and clonal T cell dynamics in site-matched human basal and squamous cell carcinomas before and after PD-1 blockade revealed that CD8+ T cells with an exhausted phenotype are more clonally expanded relative to other TILs and also expressed surface markers characteristic of tumor-reactive T cells (12). Clonal expansion of exhausted T cells in response to therapy was predominantly derived from T cell clones that were not detected in the tumor prior to therapy, and this effect was specific to exhausted T cells. Notably, most preexisting intratumoral T cell clones could be found in the tumor after therapy but did not clonally expand, and preexisting exhausted T cell clones did not adopt a nonexhausted phenotype following treatment (12). This suggests that preexisting exhausted TILs may have limited reinvigoration potential and that clonal replacement of TILs from tumor-extrinsic sources is a major aspect of ICB responses.

The cancer-immunity cycle of immune checkpoint blockade response

Immune checkpoint blockade with anti–programmed cell death 1 (anti–PD-1) therapy blocks inhibitory signaling on T cells. The immune response to PD-1 blockade relies on invigoration of tumor-extrinsic T cells during T cell priming and activation within the tumor-draining lymph node (TDLN). Activated T cells traffic to the tumor where they kill cancer cells and release antigens that are presented to T cells by dendritic cells in the TDLN, linking tumor-resident and tumor-extrinsic immune responses.

GRAPHIC: C. BICKEL/SCIENCE

Additional support for this role of tumor-extrinsic T cells comes from two studies tracking T cell clones in tumor, normal adjacent tissue, and peripheral blood. In lung, endometrial, colorectal, and renal cancers, expanded T cell clones within the tumor were commonly shared with adjacent normal tissue and peripheral blood (13). TIL clones with an exhausted phenotype were less likely to be detected in peripheral blood, suggesting that replenishment of TILs with peripheral T cells may provide a source of nonexhausted TILs. Furthermore, deep TCR profiling during neoadjuvant PD-1 blockade (prior to surgical resection) demonstrated that T cell clones that expanded in the peripheral blood following treatment were enriched within the tumor of responding patients, suggesting that expansion and subsequent infiltration of peripheral T cells may be associated with clinical response (14).

Together, these studies support a model of tumor-extrinsic T cell responses to PD-1 blockade (see the figure). Interactions between PD-L1+ cDCs and T cells in the TDLN are a compelling target for PD-1 blockade (5, 6). After priming and activation, T cells can circulate in the peripheral blood and traffic to the primary tumor site, as well as metastases. Upon cancer cell killing, the release of tumor antigens and their subsequent presentation by migratory DCs in the TDLN provide a link between the tumor-extrinsic T cell response and the cancer-immunity cycle (1). It is important to note that the tumor-extrinsic T cell response to PD-1 blockade and the reactivation of preexisting TILs are not mutually exclusive and may represent complementary or synergistic mechanisms of response.

Despite these advances, many questions remain. Although T cell clones that respond to PD-1 blockade can be found in the peripheral blood and TDLN, several possibilities regarding their precise site of activation are possible: clonal T cell priming and expansion in the TDLN and/or tertiary lymphoid sites followed by recruitment to the tumor; activation and expansion of a recently primed or unexpanded pool of progenitor T cells (such as stem cell memory or progenitor exhausted cells) within the TME and/or TDLN; or a combination of these possibilities, whereby activation of tumor-resident T cells accelerates recruitment of peripheral T cells to the TME through chemokine secretion or cDC activation. Given that most T cell proliferation in the peripheral blood occurs within 1 week of anti–PD-1 therapy and is largely diminished by 3 weeks (7, 11), what is the timing of clonal replacement? Does clonal T cell recruitment and expansion within the tumor follow the same kinetics? Chemical inhibition of T cell migration can abrogate tumor regression following ICB in some mouse models, but these results vary according to dosage and timing, indicating that such factors can influence therapeutic outcomes (4, 15).

Another area of active investigation concerns how peripheral T cell dynamics are influenced by tumor-intrinsic factors, such as tumor site and mutational heterogeneity. Skin and lung cancers have been most extensively profiled and have high amounts of immune infiltration. Comparisons between metastatic sites suggested that tumors in more immunosuppressive tissue microenvironments (such as the liver) are the least responsive to PD-1 blockade, but how tumor location influences T cell dynamics during therapy remains unclear (8). Because clonal neoantigen burden is also associated with clinical response to ICB, and TILs reactive to clonal neoantigens are present prior to treatment (1), how do clonal antigens escape immune surveillance before ICB, and what is the relationship between tumor evolution and T cell dynamics? Distinguishing general immunological effects of PD-1 blockade from antitumor immune responses will require studies pairing TIL clonotypes to their target antigens to determine how T cell phenotypes and clonal dynamics are influenced by antigen specificity.

Thus, it is possible that preexisting TILs represent a correlate, rather than a cause, of clinical responses in immune-infiltrated tumors. Namely, intratumoral immune infiltration may simply reflect TME properties such as mutational load, immunogenicity, and/or tumor site that promote continued surveillance by tumor-extrinsic T cells. Future investigations into the origins and mechanisms of response to ICB should help to identify prognostic factors underlying clinical efficacy and will facilitate the rational design of effective treatment combinations to improve responses. In particular, the combination of ICB with immune-modulating agents that amplify peripheral T cell recruitment, such as immunostimulatory agonist antibodies and cytokine-based immunotherapies, may expand the utility of ICB to a wider patient population.

Acknowledgments: A.T.S. is a scientific founder of Immunai. H.Y.C. is a cofounder of Accent Therapeutics, Boundless Bio and an adviser to 10x Genomics, Arsenal Biosciences, and Spring Discovery.

Killer T cells that 'remember' past infection boost immune response to COVID-19 variants: Study- Technology News, Firstpost

Killer T cells that ‘remember’ past infection boost immune response to COVID-19 variants: Study

  • March 31, 2021

The killer T cell responses remained largely intact, as per the study, and could recognize virtually all mutations in the variants.

Killer T cells that 'remember' past infection boost immune response to COVID-19 variants: Study

In this image, killer T cells surround a cancer cell. T-cells can ‘remember’ past infections and kill pathogens if they reappear. They are thought to have a big influence on how long people remain resistant to infection and disease. Image: NIH

The emergence of coronavirus variants has provoked concern about their impact on the effectiveness of vaccines, and whether people who were previously infected might be more susceptible to reinfection. But in welcome news, a new study on Tuesday showed that a key player in the immune response, called the “killer T cell,” remained mostly unaffected. The finding is encouraging because although these white blood cells are not a first line defense against infection, they can help prevent severe disease. Scientists at the National Institutes of Health and Johns Hopkins University analyzed blood samples from 30 people who had contracted and recovered from COVID-19 prior to the emergence of variants. They published their findings in Open Forum Infectious Diseases, an Oxford University Press journal.

The team wanted to know whether these cells, known by their technical name “CD8+ T cells,” could still recognize three variants of SARS-CoV-2: B.1.1.7, first found in Britain, B.1.351, identified in South Africa, and B.1.1.248, first seen in Brazil.

What makes each of these variants unique is the mutations they carry, especially in a region of the virus’ spike protein, structures that stud its surface and allow it to invade cells.

It has already been shown that mutations to this region of the spike protein make some variants less recognizable to neutralizing antibodies — infection fighting proteins produced by the immune system’s B cells.

This seems to be particularly true, for instance, of B.1.351, according to research on the impact of current generation COVID-19 vaccines.

Neutralizing antibodies are custom-made to fit an antigen, or a specific structure of a pathogen. In the case of the coronavirus , this is the spike protein, which the antibodies bind to, preventing the virus from infecting cells.

Killer T cells, on the other hand, look for telltale signs of cells that have already been infected with pathogens they have previously encountered, and then kill those cells.

In the new study, the researchers found that the killer T cell responses remained largely intact and could recognize virtually all mutations in the variants studied.

The researchers noted that larger studies are needed to confirm the results, but said that it nevertheless demonstrated that killer T cells are less susceptible to mutations in the coronavirus than neutralizing antibodies are.

Antibodies are still important to prevent infection in the first place — and the reduced efficacy of vaccines to the variants seems to be evidence of this.

But a killer T cell response that kicks in later and aids in clearing off the disease, helps explain why the vaccines seem to be able to prevent severe disease and hospitalization, even though their efficacy at stopping infection by variants is reduced.

Killer T cells that 'remember' past infection boost immune response to COVID-19 variants: Study- Technology News, Firstpost

Killer T cells that ‘remember’ past infection boost immune response to COVID-19 variants: Study- Technology News, Firstpost

  • March 31, 2021

The emergence of coronavirus variants has provoked concern about their impact on the effectiveness of vaccines, and whether people who were previously infected might be more susceptible to reinfection. But in welcome news, a new study on Tuesday showed that a key player in the immune response, called the “killer T cell,” remained mostly unaffected. The finding is encouraging because although these white blood cells are not a first line defense against infection, they can help prevent severe disease. Scientists at the National Institutes of Health and Johns Hopkins University analyzed blood samples from 30 people who had contracted and recovered from COVID-19 prior to the emergence of variants. They published their findings in Open Forum Infectious Diseases, an Oxford University Press journal.

The team wanted to know whether these cells, known by their technical name “CD8+ T cells,” could still recognize three variants of SARS-CoV-2: B.1.1.7, first found in Britain, B.1.351, identified in South Africa, and B.1.1.248, first seen in Brazil.

What makes each of these variants unique is the mutations they carry, especially in a region of the virus’ spike protein, structures that stud its surface and allow it to invade cells.

It has already been shown that mutations to this region of the spike protein make some variants less recognizable to neutralizing antibodies — infection fighting proteins produced by the immune system’s B cells.

This seems to be particularly true, for instance, of B.1.351, according to research on the impact of current generation COVID-19 vaccines.

Neutralizing antibodies are custom-made to fit an antigen, or a specific structure of a pathogen. In the case of the coronavirus, this is the spike protein, which the antibodies bind to, preventing the virus from infecting cells.

Killer T cells, on the other hand, look for telltale signs of cells that have already been infected with pathogens they have previously encountered, and then kill those cells.

In the new study, the researchers found that the killer T cell responses remained largely intact and could recognize virtually all mutations in the variants studied.

The researchers noted that larger studies are needed to confirm the results, but said that it nevertheless demonstrated that killer T cells are less susceptible to mutations in the coronavirus than neutralizing antibodies are.

Antibodies are still important to prevent infection in the first place — and the reduced efficacy of vaccines to the variants seems to be evidence of this.

But a killer T cell response that kicks in later and aids in clearing off the disease, helps explain why the vaccines seem to be able to prevent severe disease and hospitalization, even though their efficacy at stopping infection by variants is reduced.

Killer T cells boost immunity to coronavirus variants: study

Killer T cells boost immunity to coronavirus variants: study

  • March 30, 2021

Issued on: Modified:

Washington (AFP)

The emergence of coronavirus variants has provoked concern about their impact on the effectiveness of vaccines, and whether people who were previously infected might be more susceptible to reinfection.

But in welcome news, a new study on Tuesday showed that a key player in the immune response, called the “killer T cell,” remained mostly unaffected.

The finding is encouraging because although these white blood cells are not a first line defense against infection, they can help prevent severe disease.

Scientists at the National Institutes of Health and Johns Hopkins University analyzed blood samples from 30 people who had contracted and recovered from Covid-19 prior to the emergence of variants.

They published their findings in Open Forum Infectious Diseases, an Oxford University Press journal.

The team wanted to know whether these cells, known by their technical name “CD8+ T cells,” could still recognize three variants of SARS-CoV-2: B.1.1.7, first found in Britain, B.1.351, identified in South Africa, and B.1.1.248, first seen in Brazil.

What makes each of these variants unique is the mutations they carry, especially in a region of the virus’ spike protein, structures that stud its surface and allow it to invade cells.

It has already been shown that mutations to this region of the spike protein make some variants less recognizable to neutralizing antibodies — infection fighting proteins produced by the immune system’s B cells.

This seems to be particularly true, for instance, of B.1.351, according to research on the impact of current generation Covid vaccines.

Neutralizing antibodies are custom-made to fit an antigen, or a specific structure of a pathogen.

In the case of the coronavirus, this is the spike protein, which the antibodies bind to, preventing the virus from infecting cells.

Killer T cells, on the other hand, look for telltale signs of cells that have already been infected with pathogens they have previously encountered, and then kill those cells.

In the new study, the researchers found that the killer T cell responses remained largely intact and could recognize virtually all mutations in the variants studied.

The researchers noted that larger studies are needed to confirm the results, but said that it nevertheless demonstrated that killer T cells are less susceptible to mutations in the coronavirus than neutralizing antibodies are.

Antibodies are still important to prevent infection in the first place — and the reduced efficacy of vaccines to the variants seems to be evidence of this.

But a killer T cell response that kicks in later and aids in clearing off the disease, helps explain why the vaccines seem to be able to prevent severe disease and hospitalization, even though their efficacy at stopping infection by variants is reduced.

Cancer Cells Exploited To Aid in Their Own Destruction

Cancer Cells Exploited To Aid in Their Own Destruction

  • March 26, 2021

Immunotherapy, which recruits the body’s own immune system to attack cancer, has given many cancer patients a new avenue to treat the disease.

But many cancer immunotherapy treatments can be expensive, have devastating side effects, and only work in a fraction of patients.

Researchers at the Pritzker School of Molecular Engineering at the University of Chicago have developed a new therapeutic vaccine that uses a patient’s own tumor cells to train their immune system to find and kill cancer.

The vaccine, which is injected into the skin just like a traditional vaccine, stopped melanoma tumor growth in mouse models. It even worked long-term, destroying new tumors long after the therapy was given.

The results were published March 24 in the journal Science Advances.

“This is a new strategy for immunotherapy,” said Prof. Melody Swartz, who led the research. “It has the potential to be more efficacious, less expensive and much safer than many other immunotherapies. It is truly personalized medicine that has the potential to overcome many issues that arise with other treatments.”

Recruiting a broad immune response

In many ways, the vaccine works like a traditional flu vaccine: it uses a less-potent version of the pathogen (here, a patient’s own cancer cells, which are lethally irradiated before injection) to train the immune system to fight the disease.

However, rather than a preventive measure, this is a therapeutic vaccine, meaning it activates the immune system to destroy cancer cells anywhere in the body. To create it, Swartz and her team used melanoma cells from mice and then engineered them to secrete vascular endothelial growth factor C (VEGF-C).

VEGF-C causes tumors to strongly associate with the body’s lymphatic system, which is normally considered bad for the patient, since it can promote metastasis. But the team recently found that when tumors activate surrounding lymphatic vessels, they are much more responsive to immunotherapy and promote “bystander” T cell activation, leading to a more robust and long-lasting immune response.

The team then had to figure out how to harness the benefits of lymphatic activation in a therapeutic strategy while avoiding the potential risks of metastasis.

‘Training’ the immune system

Maria Stella Sasso, a postdoctoral fellow and first author of the paper, tested many different strategies before settling on the vaccine approach, which allowed immune “training” in a site distant from the actual tumor.

The strategy of using a patient’s own irradiated tumor cells in a therapeutic vaccine had previously been established by Glenn Dranoff and colleagues at the Novartis Institutes for BioMedical Research. Dranoff and team developed GVAX, a cancer vaccine that has been shown safe in clinical trials. Sasso decided to try this approach with VEGF-C rather than the cytokine used in GVAX. She dubbed the strategy “VEGFC-vax.”

After engineering the cells to express VEGF-C, the research team irradiated them, so they would die within a few weeks. When they injected the cells back into the skin of mice, they found that the dying tumor cells could attract and activate the immune cells, which then could recognize and kill the actual tumor cells growing on the opposite side of the mouse. Since each tumor has its own unique signature of hundreds of molecules that the immune system can recognize, the vaccine promoted a broad, robust immune response.

That led to the prevention of tumor growth in all of the mice. It also led to immunological memory, preventing new tumor growth when tumor cells were re-introduced 10 months later.

“This shows that the therapy may provide long-term efficacy against metastasis and relapse,” said Swartz, William B. Ogden Professor of Molecular Engineering.

Potential therapy for many types of cancers

Conceptually, this is the first strategy to exploit the benefits of local lymphatic vessel activation for more robust and specific immune response against tumor cells.

Unlike immunotherapeutic strategies that stimulate the immune system in a general way, such as checkpoint blockade or the many cytokines currently in preclinical development, this new immunotherapy activates only tumor-specific immune cells. Theoretically, this would avoid common side effects of immune stimulants, including immunotoxicity and even death.

And while many other cancer immunotherapies, such as CAR-T cell therapy, are tumor-specific, these strategies only work against tumor cells that express specific pre-identified tumor markers called antigens. Cancer cells can eventually overcome such treatments by shedding these markers or mutating, for example.

VEGFC-vax, however, can train immune cells to recognize a large number and variety of tumor-specific antigens. More importantly, these antigens do not need to be identified ahead of time.

The researchers are working to test this strategy on breast and colon cancers and think it could theoretically work on any type of cancer. They hope to ultimately take this therapy to clinical trials.

“We think this has huge promise for the future of personalized cancer immunotherapy,” Swartz said.

Reference: Sasso MS, Mitrousis N, Wang Y, et al. Lymphangiogenesis-inducing vaccines elicit potent and long-lasting T cell immunity against melanomas. Sci. Adv. 2021;7(13):eabe4362. doi: 10.1126/sciadv.abe4362

This article has been republished from the following materials. Note: material may have been edited for length and content. For further information, please contact the cited source.


New therapy extends breast cancer survival rate, prevents reoccurrence

New clues to classic cancer target found in immune cells

  • March 25, 2021

New clues to a long-pursued drug target in cancer may reside within immune cells, researchers at the University of Michigan Rogel Cancer Center have discovered.

The findings, which appear in Nature Immunology, not only shed new light on cancer immunology, they also suggest clinical trials related to this key target — an interaction that destabilizes the important p53 tumor suppressor protein — may unnecessarily be excluding a large number of patients.

The researchers are optimistic that the findings could help make immunotherapy treatment more effective against cancer.

“Everyone agrees this interaction is really important. The question is why, after so many years of work by biologists, biochemists and pharmacologists at universities and major drug companies, why don’t we have a drug that works?” says senior study author Weiping Zou, M.D., Ph.D., the Charles B. de Nancrede Professor of Pathology, Surgery, Immunology and Biology at the University of Michigan.

The answer, says Zou, is that it’s not just what’s happening inside a patient’s tumor cells that needs to be taken into consideration — their immune cells play a vital role, too.

“We decided to look at the problem from the perspective of immunology,” he says. “We thought that even if this important interaction is understood in tumor cells, there may still be a problem in the immune system. So we sought to better understand what was happening in T cells — the soldiers of the immune system. And what we found was quite unexpected.”

The ‘guardian of the genome’

To better understand the U-M team’s findings, it may be helpful to introduce the key players in this biological drama.

The gene TP53 has been called the “guardian of the genome” because the protein it makes — p53 — is essential for DNA repair and cell division. About half of all cancers are critically driven by mutations in this single gene that disrupt its ability to function as a tumor suppressor.

Yet that leaves another 50% of cancers that arise in patients whose tumors carry intact TP53.

For these patients, scientists have long sought to develop medicines that can disrupt the interaction between p53 and Mdm2, which is involved in keeping p53 levels in check. The idea is that disrupting their interaction would make more p53 available to suppress cancer.

These trials have generally excluded patients with p53 mutations because a lack of functional p53 means that interaction isn’t happening inside their cancers.

“You want to stop the degradation of p53, that’s the goal,” explains Zou, who is also director of the Center of Excellence for Immunology and Immunotherapy at the U-M Rogel Cancer Center. “This is a very simple concept, but people have been working on this for years and we still don’t have any FDA-approved drugs.”

This is where Zou and his colleagues tried something new. Their experiments sought to probe the interaction between p53 and Mdm2 not just inside tumor cells, but also inside immune cells.

Mdm2: bad in tumor cells, but essential in immune cells

Although disrupting the p53-Mdm2 interaction in tumor cells was generally positive, the U-M team found that if disrupting the interaction between the same proteins inside T cells results in less Mdm2 in T cells, then the T cells will be functionally impaired.

“We discovered that while Mdm2 is bad in the context of tumor cells because it gets rid of p53, it’s also essential for T cell function and survival,” Zou says. “T cells need Mdm2.”

Likewise, immunotherapy needs T cells. The approach harnesses and boosts the power of the body’s immune cells to kill cancer cells. Without working T cells, the body can’t mount an immune response. This could be one reason why immunotherapy drugs do not work in more than half of patients.

The findings also have important implications for ongoing drug discovery efforts, Zou stresses.

“Our study suggests that when you design and screen a drug candidate, you have to take not only the tumor cells into consideration, but also the T cells,” he says. “Although there’s a feeling that Mdm2 in tumor cells is a bad thing, drug developers need to make sure Mdm2 is not abolished in T cells or it will contribute to poor clinical outcomes.”

Along with experiments using mouse models lacking either MDM2 or p53 in their T cells, the scientists tested a promising new compound called APG115. APG115 interferes the interaction between Mdm2 and p53, causing an increase in Mdm2 expression in T cells. Thus, APG115 showed T cell-dependent anti-tumor activity in mouse models.

APG115 was discovered in the lab of Shaomeng Wang, Ph.D., a critical collaborator on the project and the Warner-Lambert/Parke-Davis professor and a professor of internal medicine and pharmacology at the U-M Medical School; Wang also holds an appointment in the U-M College of Pharmacy.

The compound was licensed from U-M by Ascentage Pharma and is currently in several clinical trials for the treatment of human cancer, including in combination with pembrolizumab in patients with metastatic melanomas or advanced solid tumors. Wang is a co-founder of Ascentage and its chief scientific advisor.

“This compound interferes with the interaction between p53 and Mdm2,” Zou says. “And when we administered it, we saw two things happen: p53 expression was increased, which is exactly what you want; but Mdm2 levels also increased — which was the opposite of what we expected.”

The researchers mapped the molecular interactions, finding that inside T cells, Mdm2 plays another role besides interacting with p53. It stabilizes a protein called Stat5, which is, in turn, important for T cell survival and function.

So, this paradoxical result of increasing levels of Mdm2 in T cells actually enhances their tumor-fighting properties and could make immunotherapy treatment more effective, Zou says.

Moreover, the researchers found APG115 functioned regardless of whether tumors contained normal or mutated versions of TP53.

“So what this tells us is that clinical trials for drugs that target Mdm2, including those currently in development that target the interaction between p53 and Mdm2, could potentially be expanded to include patients who are currently excluded — those whose tumors carry loss-of-function TP53 mutations,” Zou says. “Right now, if a patient’s tumor has mutated p53, then those patients wouldn’t be eligible for clinical trials for drugs that target p53-Mdm2 interaction. What our research shows is that this is really unnecessary. Patients will have normal p53 and Mdm2 in their T cells, and that’s where it’s really important.”

With this new finding, Zou and Wang believe that future clinical trials of APG115 and other Mdm2 inhibitors should include patients whose tumors harbor mutated p53.

###

Additional authors include Jiajia Zhou, Ilona Kryczek, Shasha Li, Xiong Li, Angelo Aguilar, Shuang Wei, Sara Grove, Linda Vatan, Jiali Yu, Yijian Yan, Peng Liao, Heng Lin, Jing Li, Gaopeng Li, Wan Du, Weichao Wang, Xueting Lang and Weimin Wang, all of U-M.

The research was supported in part by research grants from the National Cancer Institute (CA248430, CA217648, CA123088, CA099985, CA193136, CA152470) and the National Institutes of Health through the U-M Rogel Cancer Center Support Grant (P30CA46592).

Paper cited: “The ubiquitin ligase MDM2 sustains STAT5 stability to control T cell-mediated anti-tumor immunity,” Nature Immunology. DOI: 10.1038/s41590-021-00888-3

New therapy extends breast cancer survival rate, prevents reoccurrence

Exploiting cancer cells to aid in their own destruction

  • March 24, 2021

Immunotherapy, which recruits the body’s own immune system to attack cancer, has given many cancer patients a new avenue to treat the disease.

But many cancer immunotherapy treatments can be expensive, have devastating side effects, and only work in a fraction of patients.

Researchers at the Pritzker School of Molecular Engineering at the University of Chicago have developed a new therapeutic vaccine that uses a patient’s own tumor cells to train their immune system to find and kill cancer.

The vaccine, which is injected into the skin just like a traditional vaccine, stopped melanoma tumor growth in mouse models. It even worked long-term, destroying new tumors long after the therapy was given.

The results were published March 24 in the journal Science Advances.

“This is a new strategy for immunotherapy,” said Prof. Melody Swartz, who led the research. “It has the potential to be more efficacious, less expensive and much safer than many other immunotherapies. It is truly personalized medicine that has the potential to overcome many issues that arise with other treatments.”

Recruiting a broad immune response


In many ways, the vaccine works like a traditional flu vaccine: it uses a less-potent version of the pathogen (here, a patient’s own cancer cells, which are lethally irradiated before injection) to train the immune system to fight the disease.

However, rather than a preventive measure, this is a therapeutic vaccine, meaning it activates the immune system to destroy cancer cells anywhere in the body. To create it, Swartz and her team used melanoma cells from mice and then engineered them to secrete vascular endothelial growth factor C (VEGF-C).

VEGF-C causes tumors to strongly associate with the body’s lymphatic system, which is normally considered bad for the patient, since it can promote metastasis. But the team recently found that when tumors activate surrounding lymphatic vessels, they are much more responsive to immunotherapy and promote “bystander” T cell activation, leading to a more robust and long-lasting immune response.

The team then had to figure out how to harness the benefits of lymphatic activation in a therapeutic strategy while avoiding the potential risks of metastasis.

‘Training’ the immune system


Maria Stella Sasso, a postdoctoral fellow and first author of the paper, tested many different strategies before settling on the vaccine approach, which allowed immune “training” in a site distant from the actual tumor.

The strategy of using a patient’s own irradiated tumor cells in a therapeutic vaccine had previously been established by Glenn Dranoff and colleagues at the Novartis Institutes for BioMedical Research. Dranoff and team developed GVAX, a cancer vaccine that has been shown safe in clinical trials. Sasso decided to try this approach with VEGF-C rather than the cytokine used in GVAX. She dubbed the strategy “VEGFC-vax.”

After engineering the cells to express VEGF-C, the research team irradiated them, so they would die within a few weeks. When they injected the cells back into the skin of mice, they found that the dying tumor cells could attract and activate the immune cells, which then could recognize and kill the actual tumor cells growing on the opposite side of the mouse. Since each tumor has its own unique signature of hundreds of molecules that the immune system can recognize, the vaccine promoted a broad, robust immune response.

That led to the prevention of tumor growth in all of the mice. It also led to immunological memory, preventing new tumor growth when tumor cells were re-introduced 10 months later.

“This shows that the therapy may provide long-term efficacy against metastasis and relapse,” said Swartz, William B. Ogden Professor of Molecular Engineering.

Potential therapy for many types of cancers


Conceptually, this is the first strategy to exploit the benefits of local lymphatic vessel activation for more robust and specific immune response against tumor cells.

Unlike immunotherapeutic strategies that stimulate the immune system in a general way, such as checkpoint blockade or the many cytokines currently in preclinical development, this new immunotherapy activates only tumor-specific immune cells. Theoretically, this would avoid common side effects of immune stimulants, including immunotoxicity and even death.

And while many other cancer immunotherapies, such as CAR-T cell therapy, are tumor-specific, these strategies only work against tumor cells that express specific pre-identified tumor markers called antigens. Cancer cells can eventually overcome such treatments by shedding these markers or mutating, for example.

VEGFC-vax, however, can train immune cells to recognize a large number and variety of tumor-specific antigens. More importantly, these antigens do not need to be identified ahead of time.

The researchers are working to test this strategy on breast and colon cancers and think it could theoretically work on any type of cancer. They hope to ultimately take this therapy to clinical trials.

“We think this has huge promise for the future of personalized cancer immunotherapy,” Swartz said.

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Bacteria residing within tumor cells can boost cancer immunotherapy

Bacteria residing within tumor cells can boost cancer immunotherapy

  • March 22, 2021

Cancer immunotherapy may get a boost from an unexpected direction: bacteria residing within tumor cells. In a new study published in Nature, researchers at the Weizmann Institute of Science and their collaborators have discovered that the immune system “sees” these bacteria and shown they can be harnessed to provoke an immune reaction against the tumor.

The study may also help clarify the connection between immunotherapy and the gut microbiome, explaining the findings of previous research that the microbiome affects the success of immunotherapy.

Immunotherapy treatments of the past decade or so have dramatically improved recovery rates from certain cancers, particularly malignant melanoma; but in melanoma, they still work in only about 40% of the cases.

Prof. Yardena Samuels of Weizmann’s Molecular Cell Biology Department studies molecular “signposts” – protein fragments, or peptides, on the cell surface – that mark cancer cells as foreign and may therefore serve as potential added targets for immunotherapy. In the new study, she and colleagues extended their search for new cancer signposts to those bacteria known to colonize tumors.

Using methods developed by departmental colleague Dr. Ravid Straussman, who was one of the first to reveal the nature of the bacterial “guests” in cancer cells, Samuels and her team, led by Dr. Shelly Kalaora and Adi Nagler (joint co-first authors), analyzed tissue samples from 17 metastatic melanoma tumors derived from nine patients. They obtained bacterial genomic profiles of these tumors and then applied an approach known as HLA-peptidomics to identify tumor peptides that can be recognized by the immune system.

The research was conducted in collaboration with Dr. Jennifer A. Wargo of the University of Texas MD Anderson Cancer Center, Houston, Texas; Prof Scott N. Peterson of Sanford Burnham Prebys Medical Discovery Institute, La Jolla, California; Prof Eytan Ruppin of the National Cancer Institute, USA; Prof Arie Admon of the Technion – Israel Institute of Technology and other scientists.

The HLA peptidomics analysis revealed nearly 300 peptides from 41 different bacteria on the surface of the melanoma cells. The crucial new finding was that the peptides were displayed on the cancer cell surfaces by HLA protein complexes – complexes that are present on the membranes of all cells in our body and play a role in regulating the immune response.

One of the HLA’s jobs is to sound an alarm about anything that’s foreign by “presenting” foreign peptides to the immune system so that immune T cells can “see” them. “Using HLA peptidomics, we were able to reveal the HLA-presented peptides of the tumor in an unbiased manner,” Kalaora says. “This method has already enabled us in the past to identify tumor antigens that have shown promising results in clinical trials.”

It’s unclear why cancer cells should perform a seemingly suicidal act of this sort: presenting bacterial peptides to the immune system, which can respond by destroying these cells. But whatever the reason, the fact that malignant cells do display these peptides in such a manner reveals an entirely new type of interaction between the immune system and the tumor.

This revelation supplies a potential explanation for how the gut microbiome affects immunotherapy. Some of the bacteria the team identified were known gut microbes. The presentation of the bacterial peptides on the surface of tumor cells is likely to play a role in the immune response, and future studies may establish which bacterial peptides enhance that immune response, enabling physicians to predict the success of immunotherapy and to tailor a personalized treatment accordingly.

Moreover, the fact that bacterial peptides on tumor cells are visible to the immune system can be exploited for enhancing immunotherapy. “Many of these peptides were shared by different metastases from the same patient or by tumors from different patients, which suggests that they have a therapeutic potential and a potent ability to produce immune activation,” Nagler says.

In a series of continuing experiments, Samuels and colleagues incubated T cells from melanoma patients in a laboratory dish together with bacterial peptides derived from tumor cells of the same patient. The result: T cells were activated specifically toward the bacterial peptides.

Our findings suggest that bacterial peptides presented on tumor cells can serve as potential targets for immunotherapy. They may be exploited to help immune T cells recognize the tumor with greater precision, so that these cells can mount a better attack against the cancer. This approach can in the future be used in combination with existing immunotherapy drugs.”


Yardena Samuels, Professor, Molecular Cell Biology Department, Weizmann Institute of Science

Researchers develop new technique to more efficiently isolate and identify rare T cells

Immunologists map unknown biological machinery to produce memory T cells

  • February 27, 2021

Immunologists at St. Jude Children’s Research Hospital have mapped the previously unknown biological machinery by which the immune system generates T cells that kill bacteria, viruses, and tumor cells.

The findings have multiple implications for how the adaptive immune system responds to infections to generate such memory T cells. The experiments revealed mechanisms that inhibit the development of the long-lived memory T cells that continually renew to protect the body over time.

Blocking these inhibitory mechanisms with pharmacological or genetic approaches could boost protective immunity against infection and cancers.

The researchers also discovered a subtype of memory T cells that they named terminal effector prime cells. Mapping the pathway that controls these cells raises the possibility of manipulating this pathway to enhance the ability of the immune system to kill microbes and cancer cells.

Mapping the control pathway also provided the insight that diet may have a greater influence on immune function than previously thought.

Led by Hongbo Chi, Ph.D., of the Department of Immunology, the research appears today in the journal Cell. The first authors are Hongling Huang, Ph.D., and Peipei Zhou, Ph.D., of Immunology.

CRISPR-assisted mapping of the metabolic machinery

When the body encounters an infection, the immune system begins to generate effector T cells to attack the invading bacteria or viruses. There are two types of these T cells. One type is the memory precursor cells, which can develop into memory T cells that persist long-term to protect the body.

These are the T cells that vaccinations generate. The second type are short-lived terminal effector T cells, which have immediate cytotoxic activity.

In this study, researchers sought to map the metabolic machinery that controls how the immune system decides to produce memory T cells. Chi and his colleagues focused on the little-known mechanisms that inhibit the generation of this type of T cell.

The scientists used a gene-manipulating technology called CRISPR to sift through more than 3,000 metabolism-controlling genes in mouse cells. The goal was to discover genes that regulated the “fate” of effector T cells and memory T cells.

Nutrients play an unexpected role in T cell fate

The research revealed a previously unknown role that nutrients, such as amino acids and certain sugars, play in regulating T cell fate. To the investigators’ surprise, the analysis identified nutrient-related pathways that suppressed memory T cell production.

“The preconceived notion about nutrients’ role in immune cell function was that the cells rely on nutrients as an energy source and for building blocks,” Huang said. “But our study provides another view–that nutrients are involved in inhibitory pathways, and that deprivation of certain nutrients or metabolites might be good for adaptive immunity.

“It seems to suggest that what you eat and drink may have a greater influence on immune function than previously appreciated,” Huang said. “This will be an important pathway for future research.”

New T cell subtype identified

The studies also revealed a new subtype of effector T cell, which they named terminal effector prime cells. Blocking the development of these cells may be key to enhancing T cell-mediated immunity. The researchers’ work identified a pathway that controls the transition of developing T cells from an intermediate stage to mature terminal effector prime cells.

The researchers found they could manipulate this pathway to keep terminal effector prime cells at this intermediate stage that would induce them to proliferate to produce more memory T cells. “These findings highlight the possibility of targeting this pathway to boost protective immunity against both infections and tumors,” Chi said.

We are extremely excited by these findings. By identifying this nutrient signaling axis, our studies provide new biological insights and therapeutic targets for enhancing memory T cell responses and protective immunity against pathogens and tumors.”


Hongbo Chi, PhD, Department of Immunology, St. Jude Children’s Research Hospital

Source:

Journal reference:

Huang, H., et al. (2021) In vivo CRISPR screening reveals nutrient signaling processes underpinning CD8+ T cell fate decisions. Cell. doi.org/10.1016/j.cell.2021.02.021.

Researchers map metabolic signaling machinery for producing memory T cells

Researchers map metabolic signaling machinery for producing memory T cells

  • February 25, 2021

The researchers also discovered a subtype of memory T cells that they named terminal effector prime cells. Mapping the pathway that controls these cells raises the possibility of manipulating this pathway to enhance the ability of the immune system to kill microbes and cancer cells.

Mapping the control pathway also provided the insight that diet may have a greater influence on immune function than previously thought.

Led by Hongbo Chi, Ph.D., of the Department of Immunology, the research appears today in the journal Cell. The first authors are Hongling Huang, Ph.D., and Peipei Zhou, Ph.D., of Immunology.

CRISPR-assisted mapping of the metabolic machinery

When the body encounters an infection, the immune system begins to generate effector T cells to attack the invading bacteria or viruses. There are two types of these T cells. One type is the memory precursor cells, which can develop into memory T cells that persist long-term to protect the body. These are the T cells that vaccinations generate. The second type are short-lived terminal effector T cells, which have immediate cytotoxic activity.

In this study, researchers sought to map the metabolic machinery that controls how the immune system decides to produce memory T cells. Chi and his colleagues focused on the little-known mechanisms that inhibit the generation of this type of T cell.

The scientists used a gene-manipulating technology called CRISPR to sift through more than 3,000 metabolism-controlling genes in mouse cells. The goal was to discover genes that regulated the “fate” of effector T cells and memory T cells.

Nutrients play an unexpected role in T cell fate

The research revealed a previously unknown role that nutrients, such as amino acids and certain sugars, play in regulating T cell fate. To the investigators’ surprise, the analysis identified nutrient-related pathways that suppressed memory T cell production.

“The preconceived notion about nutrients’ role in immune cell function was that the cells rely on nutrients as an energy source and for building blocks,” Huang said. “But our study provides another view—that nutrients are involved in inhibitory pathways, and that deprivation of certain nutrients or metabolites might be good for adaptive immunity.

“It seems to suggest that what you eat and drink may have a greater influence on immune function than previously appreciated,” Huang said. “This will be an important pathway for future research.”

New T cell subtype identified

The studies also revealed a new subtype of effector T cell, which they named terminal effector prime cells. Blocking development of these cells may be key to enhancing T cell-mediated immunity. The researchers’ work identified a pathway that controls the transition of developing T cells from an intermediate stage to mature terminal effector prime cells.

The researchers found they could manipulate this pathway to keep terminal effector prime cells at this intermediate stage that would induce them to proliferate to produce more memory T cells. “These findings highlight the possibility of targeting this pathway to boost protective immunity against both infections and tumors,” Chi said.

“We are extremely excited by these findings,” Chi said. “By identifying this nutrient signaling axis, our studies provide new biological insights and therapeutic targets for enhancing memory T cell responses and protective immunity against pathogens and tumors.”

The other authors are Jun Wei, Lingyun Long, Hao Shi, Yogesh Dhungana, Nicole Chapman, Guotong Fu, Jordy Saravia, Jana Raynor, Shaofeng Liu, Gustavo Palacios, Yong-Dong Wang, Chenxi Qian and Jiyang Yu, of St. Jude.

The research was supported by the National Institutes of Health (AI105887, AI131703, AI140761, CA176624, CA221290) and ALSAC, the St. Jude fundraising and awareness organization.

 

St. Jude Children’s Research Hospital

St. Jude Children’s Research Hospital is leading the way the world understands, treats and cures childhood cancer and other life-threatening diseases. It is the only National Cancer Institute-designated Comprehensive Cancer Center devoted solely to children. Treatments developed at St. Jude have helped push the overall childhood cancer survival rate from 20 percent to 80 percent since the hospital opened more than 50 years ago. St. Jude freely shares the breakthroughs it makes, and every child saved at St. Jude means doctors and scientists worldwide can use that knowledge to save thousands more children. Families never receive a bill from St. Jude for treatment, travel, housing and food — because all a family should worry about is helping their child live. To learn more, visit stjude.org or follow St. Jude on social media at @stjuderesearch.

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