Avidity characterization of genetically engineered T-cells with novel and established approaches.

BACKGROUND: Adoptive transfer of genetically engineered autologous T-cells is becoming a successful therapy for cancer. The avidity of the engineered T-cells is of crucial importance for therapy success. We have in the past cloned a T-cell receptor (TCR) that recognizes an HLA-A2 (MHC class I)-restricted peptide from the prostate and breast cancer- associated antigen TARP. Herein we perform a side-by-side comparison of the TARP-specific TCR (TARP-TCR) with a newly cloned TCR specific for an HLA-A2-restricted peptide from the cytomegalovirus (CMV) pp65 antigen. RESULTS: Both CD8(+) T-cells and CD4(+) T-cells transduced with the HLA-A2-restricted TARP-TCR could readily be detected by multimer analysis, indicating that the binding is rather strong, since binding occured also without the CD8 co-receptor of HLA-A2. Not surprisingly, the TARP-TCR, which is directed against a self-antigen, had weaker binding to the HLA-A2/peptide complex than the CMV pp65-specific TCR (pp65-TCR), which is directed against a viral epitope. Higher peptide concentrations were needed to achieve efficient cytokine release and killing of target cells when the TARP-TCR was used. We further introduce the LigandTracer technology to study cell-cell interactions in real time by evaluating the interaction between TCR-engineered T-cells and peptide-pulsed cancer cells. We were able to successfully detect TCR-engineered T-cell binding kinetics to the target cells. We also used the xCELLigence technology to analyzed cell growth of target cells to assess the killing potency of the TCR-engineered T-cells. T-cells transduced with the pp65 - TCR exhibited more pronounced cytotoxicity, being able to kill their targets at both lower effector to target ratios and lower peptide concentrations. CONCLUSION: The combination of binding assay with functional assays yields data suggesting that TARP-TCR-engineered T-cells bind to their target, but need more antigen stimulation compared to the pp65-TCR to achieve full effector response. Nonetheless, we believe that the TARP-TCR is an attractive candidate for immunotherapy development for prostate and/or breast cancer.

Chimeric antigen receptor-engineered T cells for the treatment of metastatic prostate cancer.

Cancer immunotherapy was selected as the Breakthrough of the Year 2013 by the editors of Science, in part because of the successful treatment of refractory hematological malignancies with adoptive transfer of chimeric antigen receptor (CAR)-engineered T cells. Effective treatment of B cell leukemia may pave the road to future treatment of solid tumors, using similar approaches. The prostate expresses many unique proteins and, since the prostate gland is a dispensable organ, CAR T cells can potentially be used to target these tissue-specific antigens. However, the location and composition of prostate cancer metastases complicate the task of treating these tumors. It is therefore likely that more sophisticated CAR T cell approaches are going to be required for prostate metastasis than for B cell malignancies. Two main challenges that need to be resolved are how to increase the migration and infiltration of CAR T cells into prostate cancer bone metastases and how to counteract the immunosuppressive microenvironment found in bone lesions. Inclusion of homing (chemokine) receptors in CAR T cells may improve their recruitment to bone metastases, as may antibody-based combination therapies to normalize the tumor vasculature. Optimal activation of CAR T cells through the introduction of multiple costimulatory domains would help to overcome inhibitory signals from the tumor microenvironment. Likewise, combination therapy with checkpoint inhibitors that can reduce tumor immunosuppression may help improve efficacy. Other elegant approaches such as induced expression of immune stimulatory cytokines upon target recognition may also help to recruit other effector immune cells to metastatic sites. Although toxicities are difficult to predict in prostate cancer, severe on-target/off-tumor toxicities have been observed in clinical trials with use of CAR T cells against hematological malignancies; therefore, the choice of the target antigen is going to be crucial. This review focuses on different means of accomplishing maximal effectiveness of CAR T cell therapy for prostate cancer bone metastases while minimizing side effects and CAR T cell-associated toxicities. CAR T cell-based therapies for prostate cancer have the potential to be a therapy model for other solid tumors.

Systemic treatment with CAR-engineered T cells against PSCA delays subcutaneous tumor growth and prolongs survival of mice.

BACKGROUND: Adoptive transfer of T cells genetically engineered with a chimeric antigen receptor (CAR) has successfully been used to treat both chronic and acute lymphocytic leukemia as well as other hematological cancers. Experimental therapy with CAR-engineered T cells has also shown promising results on solid tumors. The prostate stem cell antigen (PSCA) is a protein expressed on the surface of prostate epithelial cells as well as in primary and metastatic prostate cancer cells and therefore a promising target for immunotherapy of prostate cancer. METHODS: We developed a third-generation CAR against PSCA including the CD28, OX-40 and CD3 ζ signaling domains. T cells were transduced with a lentivirus encoding the PSCA-CAR and evaluated for cytokine production (paired Student's t-test), proliferation (paired Student's t-test), CD107a expression (paired Student's t-test) and target cell killing in vitro and tumor growth and survival in vivo (Log-rank test comparing Kaplan-Meier survival curves). RESULTS: PSCA-CAR T cells exhibit specific interferon (IFN)-γ and interleukin (IL)-2 secretion and specific proliferation in response to PSCA-expressing target cells. Furthermore, the PSCA-CAR-engineered T cells efficiently kill PSCA-expressing tumor cells in vitro and systemic treatment with PSCA-CAR-engineered T cells significantly delays subcutaneous tumor growth and prolongs survival of mice. CONCLUSIONS: Our data confirms that PSCA-CAR T cells may be developed for treatment of prostate cancer.

Allogeneic lymphocyte-licensed DCs expand T cells with improved antitumor activity and resistance to oxidative stress and immunosuppressive factors.

Adoptive T-cell therapy of cancer is a treatment strategy where T cells are isolated, activated, in some cases engineered, and expanded ex vivo before being reinfused to the patient. The most commonly used T-cell expansion methods are either anti-CD3/CD28 antibody beads or the "rapid expansion protocol" (REP), which utilizes OKT-3, interleukin (IL)-2, and irradiated allogeneic feeder cells. However, REP-expanded or bead-expanded T cells are sensitive to the harsh tumor microenvironment and often short-lived after reinfusion. Here, we demonstrate that when irradiated and preactivated allosensitized allogeneic lymphocytes (ASALs) are used as helper cells to license OKT3-armed allogeneic mature dendritic cells (DCs), together they expand target T cells of high quality. The ASAL/DC combination yields an enriched Th1-polarizing cytokine environment (interferon (IFN)-γ, IL-12, IL-2) and optimal costimulatory signals for T-cell stimulation. When genetically engineered antitumor T cells were expanded by this coculture system, they showed better survival and cytotoxic efficacy under oxidative stress and immunosuppressive environment, as well as superior proliferative response during tumor cell killing compared to the REP protocol. Our result suggests a robust ex vivo method to expand T cells with improved quality for adoptive cancer immunotherapy.

T cells engineered with a T cell receptor against the prostate antigen TARP specifically kill HLA-A2+ prostate and breast cancer cells.

To produce genetically engineered T cells directed against prostate and breast cancer cells, we have cloned the T-cell receptor recognizing the HLA-A2-restricted T-cell receptor γ-chain alternate reading-frame protein (TARP)(4-13) epitope. TARP is a protein exclusively expressed in normal prostate epithelium and in adenocarcinomas of the prostate and breast. Peripheral blood T cells transduced with a lentiviral vector encoding the TARP-TCR proliferated well when exposed to peptide-specific stimuli. These cells exerted peptide-specific IFN-γ production and cytotoxic activity. Importantly, HLA-A2(+) prostate and breast cancer cells expressing TARP were also killed, demonstrating that the TARP(4-13) epitope is a physiologically relevant target for T-cell therapy of prostate and breast cancer. In conclusion, we present the cloning of a T cell receptor (TCR) directed against a physiologically relevant HLA-A2 epitope of TARP. To our knowledge this report on engineering of T cells with a TCR directed against an antigen specifically expressed by prostate cells is unique.