Phase I Trial of Anti-PSMA Designer CAR-T Cells in Prostate Cancer: Possible Role for Interacting Interleukin 2-T Cell Pharmacodynamics as a Determinant of Clinical Response

BACKGROUND

Chimeric antigen receptor (CAR)-modified "designer" T cells (dTc, CAR-T) against PSMA selectively target antigen-expressing cells in vitro and eliminate tumors in vivo. Interleukin 2 (IL2), widely used in adoptive therapies, was proven essential in animal models for dTc to eradicate established solid tumors.

METHODS

Patients under-went chemotherapy condi-tion-ing, followed by dTc dosing under a Phase I escalation with continuous infusion low dose IL2 (LDI). A target of dTc escalation was to achieve ≥20% engraftment of infused activated T cells.

RESULTS

Six patients enrolled with doses prepared of whom five were treated. Patients received 10(9) or 10(10) autologous T cells, achieving expansions of 20-560-fold over 2 weeks and engraftments of 5-56%. Pharmacokinetic and pharmacodynamic analyses established the impact of conditioning to promote expansion and engraftment of the infused T cells. Unexpectedly, administered IL2 was depleted up to 20-fold with high engraftments of activated T cells (aTc) in an inverse correlation (P < 0.01). Clinically, no anti-PSMA toxicities were noted, and no anti-CAR reactivities were detected post-treatment. Two-of-five patients achieved clinical partial responses (PR), with PSA declines of 50% and 70% and PSA delays of 78 and 150 days, plus a minor response in a third patient. Responses were unrelated to dose size (P = 0.6), instead correlating inversely with engraftment (P = 0.06) and directly with plasma IL2 (P = 0.03), suggesting insufficient IL2 with our LDI protocol to support dTc anti-tumor activity under optimal (high) dTc engraftments.

CONCLUSIONS

Under a Phase I dose escalation in prostate cancer, a 20% engraftment target was met or exceeded in three subjects with adequate safety, leading to study conclusion. Clinical responses were obtained but were suggested to be restrained by low plasma IL2 when depleted by high levels of engrafted activated T cells. This report presents a unique example of how the pharmaco-dynamics of "drug-drug" interactions may have a critical impact on the efficacy of their co-application. A new Pilot/Phase II trial is planned to test moderate dose IL2 (MDI) together with high dTc engraftments for anticipated improved therapeutic efficacy. Prostate 76:1257-1270, 2016. © 2016 Wiley Periodicals, Inc.

A Perspective of Immunotherapy for Prostate Cancer

In cancer patients, the immune system is often altered with an excess of inhibitory factors, such as immunosuppressive cytokines, produced by regulatory T cells (Treg) or myeloid-derived suppressor cells (MDSC). The manipulation of the immune system has emerged as one of new promising therapies for cancer treatment, and also represents an attractive strategy to control prostate cancer (PCa). Therapeutic cancer vaccines and immune checkpoint inhibitors have been the most investigated in clinical trials. Many trials are ongoing to define the effects of immune therapy with established treatments: androgen deprivation therapy (ADT) and chemotherapy (CT) or radiotherapy (RT). This article discusses some of these approaches in the context of future treatments for PCa.

Immunotherapeutic approaches in prostate cancer: combinations and clinical integration

Despite multiple immunologic approaches with peptide, protein, and DNA vaccines, no single therapy has induced complete remission or maintained durability of response in patients with castration-resistant prostate cancer (CRPC). Historically, immunotherapy has had limited effect on solid tumors with the exception of melanoma and renal cell carcinomas, which have been deemed as immunologic cancers given their potential for remissions either spontaneously or after removal of the primary lesion. There is considerable excitement about using an immunotherapy in combination with biologic agents such as checkpoint inhibitors, cytokines, other vaccines, or chemotherapy. Sipuleucel-T represents one of several novel immunologic therapeutic approaches to treat prostate cancer in addition to other solid tumors. It is the first in its class of autologous cellular therapies to demonstrate safety and an overall survival benefit in patients with asymptomatic or minimally symptomatic CRPC and represents a unique treatment method that may be further enhanced with other agents. Although sipuleucel-T can be used as a foundation on which to build and enhance future immunologic clinical trials, other exciting strategies are in development that may be easily integrated into the algorithm of current care.

Immunotherapy in metastatic prostate cancer

INTRODUCTION

Prostate cancer remains a challenge as a target for immunological approaches. The approval of the first cell-based immune therapy, Sipuleucel-T for prostate cancer introduced prostate cancer as a solid tumor with the potential to be influenced by the immune system.

METHODS

We reviewed articles on immunological management of prostate cancer and challenges that lie ahead for such strategies.

RESULTS

Treatments have focused on the identification of novel cell surface antigens thought to be unique to prostate cancer. These include vaccines against carbohydrate and blood group antigens, xenogeneic and naked DNA vaccines, and pox viruses used as prime-boost or checkpoint inhibitors. No single vaccine construct to date has resulted in a dramatic antitumor effect. The checkpoint inhibitor, anti-CTLA-4 has resulted in several long-term remissions, but phase III trials have not demonstrated an antitumor effect or survival benefit.

CONCLUSIONS

Multiple clinical trials suggest that prostate cancer may not be optimally treated by single agent immune therapies and that combination with biologic agents, chemotherapies, or radiation may offer some enhancement of benefit.