Caitlin Creasy

Loss of PTEN promotes resistance to T cell–mediated immunotherapy

UNLABELLED T cell-mediated immunotherapies are promising cancer treatments. However, most patients still fail to respond to these therapies. The molecular determinants of immune resistance are poorly understood. We show that loss of PTEN in tumor cells in preclinical models of melanoma inhibits T cell-mediated tumor killing and decreases T-cell trafficking into tumors. In patients, PTEN loss correlates with decreased T-cell infiltration at tumor sites, reduced likelihood of successful T-cell expansion from resected tumors, and inferior outcomes with PD-1 inhibitor therapy. PTEN loss in tumor cells increased the expression of immunosuppressive cytokines, resulting in decreased T-cell infiltration in tumors, and inhibited autophagy, which decreased T cell-mediated cell death. Treatment with a selective PI3Kβ inhibitor improved the efficacy of both anti-PD-1 and anti-CTLA-4 antibodies in murine models. Together, these findings demonstrate that PTEN loss promotes immune resistance and support the rationale to explore combinations of immunotherapies and PI3K-AKT pathway inhibitors. SIGNIFICANCE This study adds to the growing evidence that oncogenic pathways in tumors can promote resistance to the antitumor immune response. As PTEN loss and PI3K-AKT pathway activation occur in multiple tumor types, the results support the rationale to further evaluate combinatorial strategies targeting the PI3K-AKT pathway to increase the efficacy of immunotherapy.

Manipulating the tumor microenvironment ex vivo for enhanced expansion of tumor-infiltrating lymphocytes for adoptive cell therapy

Purpose: Cultured tumor fragments from melanoma metastases have been used for years as a source of tumor-infiltrating lymphocytes (TIL) for adoptive cell therapy (ACT). The expansion of tumor-reactive CD8+ T cells with interleukin-2 (IL2) in these early cultures is critical in generating clinically active TIL infusion products, with a population of activated 4-1BB CD8+ T cells recently found to constitute the majority of tumor-specific T cells. Experimental Design: We used an agonistic anti–4-1BB antibody added during the initial tumor fragment cultures to provide in situ 4-1BB costimulation. Results: We found that addition of an agonistic anti–4-1BB antibody could activate 4-1BB signaling within early cultured tumor fragments and accelerated the rate of memory CD8+ TIL outgrowth that were highly enriched for melanoma antigen specificity. This was associated with NFκB activation and the induction of T-cell survival and memory genes, as well as enhanced IL2 responsiveness, in the CD8+ T cells in the fragments and emerging from the fragments. Early provision of 4-1BB costimulation also affected the dendritic cells (DC) by activating NFκB in DC and promoting their maturation inside the tumor fragments. Blocking HLA class I prevented the enhanced outgrowth of CD8+ T cells with anti–4-1BB, suggesting that an ongoing HLA class I–mediated antigen presentation in early tumor fragment cultures plays a role in mediating tumor-specific CD8+ TIL outgrowth. Conclusions: Our results highlight a previously unrecognized concept in TIL ACT that the tumor microenvironment can be dynamically regulated in the initial tumor fragment cultures to regulate the types of T cells expanded and their functional characteristics. Clin Cancer Res; 21(3); 611–21. ©2014 AACR.

Metastatic melanoma patient had a complete response with clonal expansion after whole brain radiation and PD-1 blockade

This case report provides a rationale for a carefully timed combination of WBRT + anti-PD-1 for the treatment of metastatic melanoma patients with brain metastases, as well as for other cancers for which anti–PD-1 has been approved. We report here on a patient with metastatic melanoma who had extensive brain metastases. After being treated with the sequential combination of whole brain radiation therapy followed by the PD-1–inhibitory antibody, pembrolizumab, the patient had a durable complete response. Retrospective laboratory studies of T cells revealed that, after treatment with anti-PD-1 commenced, effector CD8+ T cells in the blood expanded and the ratio of CD8+:Treg T cells increased. A CD8+ T-cell clone present in the initial brain metastases was expanded in the blood after anti-PD-1 treatment, which suggested an antitumor role for this clone. Immunohistochemical analysis confirmed the presence of CD8+ T cells and low PD-L1 expression in the brain metastases before immunotherapy initiation. This sequence of therapy may provide an option for melanoma patients with unresponsive brain metastases. Cancer Immunol Res; 5(2); 100–5. ©2017 AACR.

Thoracic and Abdominal Lymphatic Pump Techniques Inhibit the Growth of S. pneumoniae Bacteria in the Lungs of Rats

BACKGROUND Osteopathic physicians utilize manual medicine techniques called lymphatic pump techniques (LPT) to improve lymphatic flow and enhance immunity. Clinical studies report that LPT enhances antibody responses to bacterial vaccines, shortens duration of cough in patients with respiratory disease, and shortens the duration of intravenous antibiotic therapy and hospital stay in patients with pneumonia. The purpose of this study was to identify if thoracic LPT (Th-LPT) or abdominal LPT (Ab-LPT) would reduce Streptococcus pneumoniae colony-forming units (CFU) in the lungs of rats with acute pneumonia. METHODS AND RESULTS Rats were nasally infected with S. pneumoniae and received either control, sham, Ab-LPT, or Th-LPT once daily for 3 consecutive days. On day 4 post-infection, lungs were removed and bacteria were enumerated. Three daily applications of either Ab-LPT or Th-LPT were able to significantly (p<0.05) reduce the numbers of pulmonary bacteria compared to control and sham. There were no significant differences in the percentage or concentration of leukocytes in blood between groups, suggesting neither Ab-LPT nor Th-LPT release leukocytes into blood circulation. CONCLUSIONS Our data demonstrate that LPT may protect against pneumonia by inhibiting bacterial growth in the lung; however, the mechanism of protection is unclear. Once these mechanisms are understood, LPT can be optimally applied to patients with pneumonia, which may substantially reduce morbidity, mortality, and frequency of hospitalization.

IL2 Variant Circumvents ICOS+ Regulatory T-cell Expansion and Promotes NK Cell Activation

IL2 is not commonly used as immunotherapy due to its induction of regulatory T cells and dangerous cytokine storms. The IL2 variant, F42K, promoted the expansion and activation of antitumor NK cells without inducing highly suppressive Tregs. Clinical responses to high-dose IL2 therapy are limited due to selective expansion of CD4+CD25+Foxp3+ T-regulatory cells (Treg), especially ICOS+ Tregs, rather than natural killer (NK) cells and effector T cells. These ICOS+ Tregs are highly suppressive and constitutively express high levels of IL2Rα (CD25) and CD39. Here, we characterized the effect of a mutant form of IL2 (F42K), which preferentially binds to the lower affinity IL2Rβγ with reduced binding to CD25, on Tregs, effector NK cells, and T-cell subsets. Unlike wild-type (WT) IL2, F42K did not efficiently induce the expansion of highly suppressive ICOS+ Tregs in peripheral blood mononuclear cells (PBMC) from healthy controls and melanoma patients. Instead, it promoted the expansion of CD16+CD56+ NK cells and CD56hiCD16− NK cell subsets in both short- and long-term cultures, with enhanced Bcl-2 expression. Stimulation of PBMCs with F42K induced expression of more NK cell activation molecules, such as NKp30, NKp44, DNAM-1, NKG2D, 4-1BB/CD137, and Tim-3, than WT IL2. F42K induced greater upregulation of TRAIL, and NK-mediated cytolytic activity was increased against both autologous and HLA-mismatched melanoma cells compared with WT IL2. Gene expression analysis revealed distinct gene expression profiles stimulated by F42K, WT IL2, and IL15. F42K therapy in vivo also induced a dramatic reduction in the expansion of ICOS+ Tregs, promoted NK cell expansion, and inhibited melanoma tumor growth more efficiently than WT IL2 and more effectively than anti–CTLA-4. Our findings suggest that F42K could be a potential substitute for WT IL2 as a cytokine therapy for cancer. Cancer Immunol Res; 4(11); 983–94. ©2016 AACR.

Lymphatic Pump Treatment as an Adjunct to Antibiotics for Pneumonia in a Rat Model

BACKGROUND Lymphatic pump treatment (LPT) is a technique used by osteopathic physicians as an adjunct to antibiotics for patients with respiratory tract infections, and previous studies have demonstrated that LPT reduces bacterial load in the lungs of rats with pneumonia. Currently, it is unknown whether LPT affects drug effcacy. OBJECTIVE To determine whether the combination of antibiotics and LPT would reduce bacterial load in the lungs of rats with acute pneumonia. METHODS Rats were infected intranasally with 5×107 colony-forming units (CFU) of Streptococcus pneumoniae. At 24, 48, and 72 hours after infection, the rats received no therapy (control), 4 minutes of sham therapy, or 4 minutes of LPT, followed by subcutaneous injection of 40 mg/kg of levofoxacin or sterile phosphate-buffered saline. At 48, 72, and 96 hours after infection, the spleens and lungs were collected, and S pneumoniae CFU were enumerated. Blood was analyzed for a complete blood cell count and leukocyte differential count. RESULTS At 48 and 72 hours after infection, no statistically significant differences in pulmonary CFU were found between control, sham therapy, or LPT when phosphate-buffered saline was administered; however, the reduction in CFU was statistically significant in all rats given levofoxacin. The combination of sham therapy and levofoxacin decreased bacterial load at 72 and 96 hours after infection, and LPT and levofoxacin significantly reduced CFU compared with sham therapy and levofoxacin at both time points (P<.05). Colony-forming units were not detected in the spleens at any time. No statistically significant differences in hematologic findings between any treatment groups were found at any time point measured. CONCLUSION The results suggest that 3 applications of LPT induces an additional protective mechanism when combined with levofoxacin and support its use as an adjunctive therapy for the management of pneumonia; however, the mechanism responsible for this protection is unclear.

SLC45A2: A Melanoma Antigen with High Tumor Selectivity and Reduced Potential for Autoimmune Toxicity

T cell–based immunotherapy against melanoma-associated antigens can result in on-target/off-tumor cytotoxicity. SLC45A2, a protein overexpressed in melanoma compared with normal melanocytes, was identified as a T-cell target that may be less prone to inducing autoimmune side effects. Cytotoxic T lymphocyte (CTL)–based immunotherapies have had remarkable success at generating objective clinical responses in patients with advanced metastatic melanoma. Although the melanocyte differentiation antigens (MDA) MART-1, PMEL, and tyrosinase were among the first melanoma tumor-associated antigens identified and targeted with immunotherapy, expression within normal melanocytes of the eye and inner ear can elicit serious autoimmune side effects, thus limiting their clinical potential as CTL targets. Using a tandem mass spectrometry (MS) approach to analyze the immunopeptidomes of 55 melanoma patient–derived cell lines, we identified a number of shared HLA class I–bound peptides derived from the melanocyte-specific transporter protein SLC45A2. Antigen-specific CTLs generated against HLA-A*0201- and HLA-A*2402–restricted SLC45A2 peptides effectively killed a majority of HLA-matched cutaneous, uveal, and mucosal melanoma cell lines tested (18/25). CTLs specific for SLC45A2 showed significantly reduced recognition of HLA-matched primary melanocytes that were, conversely, robustly killed by MART1- and PMEL-specific T cells. Transcriptome analysis revealed that SLC45A2 mRNA expression in normal melanocytes was less than 2% that of other MDAs, therefore providing a more favorable melanoma-to-melanocyte expression ratio. Expression of SLC45A2 and CTL sensitivity could be further upregulated in BRAF(V600E)-mutant melanoma cells upon treatment with BRAF or MEK inhibitors, similarly to other MDAs. Taken together, our study demonstrates the feasibility of using tandem MS as a means of discovering shared immunogenic tumor-associated epitopes and identifies SLC45A2 as a promising immunotherapeutic target for melanoma with high tumor selectivity and reduced potential for autoimmune toxicity. Cancer Immunol Res; 5(8); 618–29. ©2017 AACR.

Prospective Analysis of Adoptive TIL Therapy in Patients with Metastatic Melanoma: Response, Impact of Anti-CTLA4, and Biomarkers to Predict Clinical Outcome

Purpose: Adoptive cell therapy (ACT) using tumor-infiltrating lymphocytes (TIL) has consistently demonstrated clinical efficacy in metastatic melanoma. Recent widespread use of checkpoint blockade has shifted the treatment landscape, raising questions regarding impact of these therapies on response to TIL and appropriate immunotherapy sequence. Patients and Methods: Seventy-four metastatic melanoma patients were treated with autologous TIL and evaluated for clinical response according to irRC, overall survival, and progression-free survival. Immunologic factors associated with response were also evaluated. Results: Best overall response for the entire cohort was 42%; 47% in 43 checkpoint-naïve patients, 38% when patients were exposed to anti-CTLA4 alone (21 patients) and 33% if also exposed to anti-PD1 (9 patients) prior to TIL ACT. Median overall survival was 17.3 months; 24.6 months in CTLA4-naïve patients and 8.6 months in patients with prior CTLA4 blockade. The latter patients were infused with fewer TIL and experienced a shorter duration of response. Infusion of higher numbers of TIL with CD8 predominance and expression of BTLA correlated with improved response in anti-CTLA4 naïve patients, but not in anti-CTLA4 refractory patients. Baseline serum levels of IL9 predicted response to TIL ACT, while TIL persistence, tumor recognition, and mutation burden did not correlate with outcome. Conclusions: This study demonstrates the deleterious effects of prior exposure to anti-CTLA4 on TIL ACT response and shows that baseline IL9 levels can potentially serve as a predictive tool to select the appropriate sequence of immunotherapies. Clin Cancer Res; 24(18); 4416–28. ©2018 AACR.

4-1BB Agonist Focuses CD8+ Tumor-Infiltrating T-Cell Growth into a Distinct Repertoire Capable of Tumor Recognition in Pancreatic Cancer

Purpose: Survival for pancreatic ductal adenocarcinoma (PDAC) patients is extremely poor and improved therapies are urgently needed. Tumor-infiltrating lymphocyte (TIL) adoptive cell therapy (ACT) has shown great promise in other tumor types, such as metastatic melanoma where overall response rates of 50% have been seen. Given this success and the evidence showing that T-cell presence positively correlates with overall survival in PDAC, we sought to enrich for CD8+ TILs capable of autologous tumor recognition. In addition, we explored the phenotype and T-cell receptor repertoire of the CD8+ TILs in the tumor microenvironment. Experimental Design: We used an agonistic 4-1BB mAb during the initial tumor fragment culture to provide 4-1BB costimulation and assessed changes in TIL growth, phenotype, repertoire, and antitumor function. Results: Increased CD8+ TIL growth from PDAC tumors was achieved with the aid of an agonistic 4-1BB mAb. Expanded TILs were characterized by an activated but not terminally differentiated phenotype. Moreover, 4-1BB stimulation expanded a more clonal and distinct CD8+ TIL repertoire than IL2 alone. TILs from both culture conditions displayed MHC class I-restricted recognition of autologous tumor targets. Conclusions: Costimulation with an anti-4-1BB mAb increases the feasibility of TIL therapy by producing greater numbers of these tumor-reactive T cells. These results suggest that TIL ACT for PDAC is a potential treatment avenue worth further investigation for a patient population in dire need of improved therapy. Clin Cancer Res; 23(23); 7263–75. ©2017 AACR.

Combined analysis of antigen presentation and T cell recognition reveals restricted immune responses in melanoma

The quest for tumor-associated antigens (TAA) and neoantigens is a major focus of cancer immunotherapy. Here, we combine a neoantigen prediction pipeline and human leukocyte antigen (HLA) peptidomics to identify TAAs and neoantigens in 16 tumors derived from seven patients with melanoma and characterize their interactions with their tumor-infiltrating lymphocytes (TIL). Our investigation of the antigenic and T-cell landscapes encompassing the TAA and neoantigen signatures, their immune reactivity, and their corresponding T-cell identities provides the first comprehensive analysis of cancer cell T-cell cosignatures, allowing us to discover remarkable antigenic and TIL similarities between metastases from the same patient. Furthermore, we reveal that two neoantigen-specific clonotypes killed 90% of autologous melanoma cells, both in vitro and in vivo, showing that a limited set of neoantigen-specific T cells may play a central role in melanoma tumor rejection. Our findings indicate that combining HLA peptidomics with neoantigen predictions allows robust identification of targetable neoantigens, which could successfully guide personalized cancer immunotherapies.Significance: As neoantigen targeting is becoming more established as a powerful therapeutic approach, investigating these molecules has taken center stage. Here, we show that a limited set of neoantigen-specific T cells mediates tumor rejection, suggesting that identifying just a few antigens and their corresponding T-cell clones could guide personalized immunotherapy. Cancer Discov; 8(11); 1366-75. ©2018 AACR. This article is highlighted in the In This Issue feature, p. 1333.