A research team headed by scientists at the San Raffaele-Telethon Institute for Gene Therapy (SR-TIGET, Milan) has identified what they say is a powerful strategy to rejuvenate the effectiveness of chimeric antigen receptor (CAR) T cell therapy against glioblastoma (GBM), one of the most lethal and treatment-resistant brain tumors. Led by Nadia Coltella, PhD, and Luigi Naldini, MD, PhD, the preclinical study findings highlight how gene therapy targeting immune stimulating cytokines to the tumor microenvironment (TME) and enabling their private cross-talk with CAR-T cells restores CAR-T killer activity and boosts a broader immune response that inhibits tumor growth and extends host survival in murine glioblastoma models.
“Solid tumors like glioblastoma have been notoriously difficult for CAR-T cells to penetrate and control,” commented Federico Rossari, PhD, who is first author of the team’s published study in Science Translational Medicine “A cross-talk established by tumor-targeted cytokines rescues CAR T cell activity and engages host T cells against glioblastoma in mice.” Rossari added, “By reprogramming a population of tumor-infiltrating macrophages to deliver cytokines directly into the tumor, we’ve morphed the immunosuppressive TME into one supportive of immune cells, thus allowing CAR T cells to better persist, become activated and attack tumor cells.”
In their paper the team concluded “Here, we show that CAR T cells against the clinically relevant antigen B7-H3 are rescued in the hostile GBM TME by tumor-targeted cytokine delivery and can achieve therapeutic efficacy in an immunocompetent GBM model that did not respond to CAR T cells alone.”
CAR-T cells have shown “transformative results” in blood cancers but have struggled in solid tumors due to the hostile, immunosuppressive TME, the authors commented. “Chimeric antigen receptor (CAR) T cells have shown limited efficacy against solid tumors because of poor tissue penetration, constrained activity, and early exhaustion due to the immunosuppressive tumor microenvironment (TME).” And while stimulatory cytokines can counteract immune suppression, their systemic administration can carry the risk of toxicities and counter-regulatory responses because of immune hyperactivation.
The team’s newly reported strategy leads to selective release of two cytokines within the TME. “… we leveraged a population of tumor-associated TIE2-expressing macrophages (TEMs) to release interferon-α (IFN-α) and/or orthogonal interleukin-2 (oIL2) at the tumor site,” they explained. They describe interferon-α as a pleiotropic immune stimulator that counteracts local immune suppressive cues and enforces antigen presentation and immune effectors’ activity. The other cytokine, orthogonal interleukin-2, is an engineered mutant of interleukin-2 that can only activate a cognate mutant receptor co-introduced with the CAR into T cells, and so boosts the proliferation specifically of the administered effector engaged in fighting the tumor.
The researchers found that in a mouse model of glioblastoma that mimics the pathology and immunological barriers seen in human patients, the targeted cytokines rescued the activity of CAR T cells that, given alone, were ineffective – as mostly seen in clinical trials. In turn, the rescued CAR T cells now synergized with cytokine delivery, significantly enhancing their effect on delaying tumor growth and extending mouse survival. “Targeted cytokine delivery rescued CAR T cell functionality against the clinically relevant tumor antigen B7-homolog 3 (B7-H3) in an orthotopic, CAR T cell–refractory, immunocompetent mouse model of glioblastoma (GBM) named mGB2 that recapitulates pathological features of the human disease,” the team explained.
Strikingly, even tumors with only a fraction of cells expressing the CAR-targeted antigen B7-H3 were effectively controlled, indicating engagement of endogenous T cells on top of the CAR T to fight the tumor. “Furthermore, IFN-α, especially when combined with private oIL2 signaling to CAR T cells, elicited potent endogenous T cell responses against multiple tumor-associated antigens, leading to delayed GBM growth and prolonged mouse survival even with tumors expressing B7-H3 in only a fraction of cells,” the authors reported.
“We observed not only reactivation of the CAR-T cells but also the recruitment of the host’s own T cells against a wider range of tumor antigens,” added senior co-corresponding author Coltella. “This phenomenon, known as antigenic spreading, was mostly dependent on IFN-α activity in the TME and is a key feature for creating effective immunity as it may overcome immune evasion by tumors targeted only through a single antigen by the CAR-T cells.”
Giorgio Alvisi, PhD, co-first author of the study, commented, “The private ‘cross-talk’ between genetically engineered macrophages and CAR T cells established in the TME ensures that the immune stimulants act only where needed, sparing the rest of the body from systemic toxicity, and specifically on the relevant target cells involved in the tumor attack, again preventing collateral damage and aberrant effects.”
The newly published study builds on prior developments by the Naldini laboratory of a gene therapy strategy that exploit genetic engineering of hematopoietic progenitors to generate a progeny of monocyte/macrophages that selectively release their immune stimulating payload upon infiltrating a tumor. This strategy has been taken to its first-in-human clinical testing as stand-alone treatment of glioblastoma by the biotech company Genenta Science, a spin-off from the San Raffaele Institute.
“This work represents another important step forward in our decade-long commitment to develop a novel gene and cell therapy strategy effective against tumors, as we have been able to do for several genetic diseases along the life of our institute” stated Naldini, MD, PhD, Director of SR-TIGET and Professor at Università Vita-Salute San Raffaele.
“The tumor-targeted IFN-α delivery strategy is already being evaluated as stand-alone treatment in a first-in-human phase 1/2a trial on the most aggressive type of glioblastoma (Temferon trial) led by the biotech company Genenta Science,” Naldini explained. The authors of the newly released study further noted, “Interim data from the Temferon clinical trial (NCT03866109, Genenta Science) demonstrated the safety and tolerability of the approach with absence of dose-limiting toxicities and evidence of reprogramming of the TME.”
Naldini continued. “The study has shown feasibility, safety, biological activity in reprogramming the TME and early but promising indication of therapeutic benefit, albeit limited by the small number of treated patients and the design of a phase 1 study. A combination of Temferon with CAR-T cells administration, as prompted by our new study, could in future further enhance the benefit of the treatment and broaden its efficacy to a larger fraction of patients.”
