Weaponizing the Immune System to Cure HIV Infection and Cancer

Developing next generation CAR-T cell treatments to cure HIV and cancer. Our laboratory is utilizing novel molecular, cellular and biochemical approaches to weaponize the immune system by using an artificial immunity (AI) strategy to boost immune response to treat infectious diseases and cancer.  One strategy we are utilizing is to develop novel CAR-T cells for infusion into people living with HIV (PLWH) which can control HIV infection by efficiently eliminating HIV-infected cells. The development of combinational antiretroviral therapy (ART) which targets different steps in the HIV replication cycle has enabled long-term survival of PLWH. However, despite long-term reduction of HIV to undetectable levels, resurgence of viremia occurs soon after the cessation of ART demonstrating that years of successful suppression of active viral replication did not cure HIV infection. HIV cure was prevented by the presence of HIV reservoirs consisting of latent HIV-infected cells distributed throughout the body, which survive despite standard or intensified ART and can produce infectious virus and reintroduce HIV infection after the cessation of ART.  Nevertheless, HIV has been cured in a few PLWH after transplantation of allogeneic hematopoietic stem cells from donors whose T cells are resistant to HIV infection due to a homozygous mutation in the HIV coreceptor, CCR5. This breakthrough demonstrated that HIV could be cured. However, the high morbidity and mortality associated with bone marrow transplantation limits the routine application of this approach and provides a strong rationale for pursuing alternative strategies for providing ART-free HIV remission by leveraging observations that potent HIV-specific immune responses could provide sustained ART-free remission in PLWH.

The capacity of chimeric antigen receptor (CAR)-T cells engineered to target malignant cells to induce remission and cure in cancer patients made this an attractive approach to provide PLWH with a potent HIV-specific immune response.   Our lab has collaborated with the Caring Cross group to develop, optimize and validate the duo-CAR architecture which co-express two independent CARs (duoCAR-T cells), each recognizing a different gp120 epitope and linked to a different costimulatory signaling domain. We demonstrated that this architecture which targets two highly conserved gp120 epitopes, the CD4 binding site for the HIV gp120 envelope and the HIV co-receptor binding region, enables duoCAR-T cells to be extremely resistant to HIV infection and markedly inhibit in vivo HIV infection by a broad range of variants, which should deter HIV immune escape. After validating the in vitro efficacy of these duoCAR-T cells in tissue culture, we used a humanized mouse model we developed that supports HIV infection to demonstrate the in vivo ability of the duoCAR-T cells to control HIV infection. This data was crucial for supporting the approval of this treatment by the FDA for advancement into clinical trials. The duoCAR-T-cell therapy is currently being evaluated in an ongoing phase I/IIa clinical trial with PLWH (NCT04648046). We are currently developing the next generation of duoCAR-T cells which display increased potency and persistence. In addition, we are developing a new generation of CAR-T cells that we engineered by transduction with antibody-encoding lentiviral gene vectors (LV) enabling T cells which confer them with the ability to produce broadly neutralizing antibodies capable of potently suppressing HIV infection. These CAR-T-B cells can deliver a one-two punch to control HIV infection by not only killing cells already infected with HIV, but also preventing the further spread of infection.

Developing immunobiologics which deliver antigen-specific and co-stimulatory signals to focally activate HIV- and cancer-specific CTLs. Another strategy we are using to weaponize the immune system is a modular biologic platform termed Immuno-STAT (IST), that selectively expands antigen-specific T cells by delivering antigen-specific TCR and co-stimulatory signals through HLA-A2 MHC molecules covalently-tethered to pathogen-derived peptides (pMHC) and linked CD28- or 4-1BB-specific ligands, respectively. These biologics were developed by the Almo lab and immunologically and functionally validated by our lab as an immunotherapeutic for the in vivo expansion of antigen-specific CTL to eliminate virally infected or cancerous cells. The immune response of naïve CD8+ T cells is initiated by three coordinated signals delivered by antigen-presenting cells: Signal 1 delivered by engagement between antigen-specific TCR and its cognate peptide-MHC complex (pMHC); Signal 2 provided by co-stimulatory receptors, such as CD28 and 4-1BB, through interactions with the B7 and 4-1BBL ligands, respectively; and Signal 3 supplied by cytokines, such as IL-7, IL-21, IL-2, or IL-15, which modulate cellular proliferation and differentiation. We demonstrated that ISTs carrying a pMHC alone, a pMHC linked to a CD28 agonist, or pMHC linked to a 4-1BB agonist were all able to induce activation and selective expansion of cytotoxic virus-specific memory CD8+ T cells in vitro and to potently suppressed in vitro and in vivo HIV and CMV infection.

             In addition to using these IST as an immunotherapeutic, we are also using them to delineate the minimum signals required to activate and expand antigen-specific memory CD8+ T cells because they can specifically deliver a T cell receptor (TCR) signal alone or paired with a defined co-stimulatory signal to naïve and memory antigen-specific CD8+ T cells. Using a reductionist approach that provides defined TCR and co-stimulatory signaling, we demonstrated that different IST could engage TCR alone or in combination with either CD28 or 4-1BB costimulatory to initiate distinct transcriptional programs in memory CMV-specific CD8+ T cells. As compared to activation by TCR signaling alone, the combination of TCR and CD28 or 4-1BB co-stimulatory signals significantly altered the transcriptome and drove expression of genes related to growth and survival. Nevertheless, TCR signaling alone was sufficient for robust recall activation and expansion of functional cytomegalovirus CMV-specific and HIV-specific memory CD8+ T cells. This response contrasts with naïve CD8+ T cells, which required CD28 co-stimulation in addition to TCR stimulation for antigen-specific activation. These results have important implications for antigen-specific immunotherapy by indicating that biologics that deliver TCR signals alone may be sufficient for immunotherapeutic strategies designed to expand memory CD8+ T cells to eliminate cancerous or infected cells. However, strategies that aim to stimulate naïve T cell responses would require the codelivery of TCR and CD28 signals.

             We leveraged these findings to applying the IST for developing a new strategy for expanding antigen-specific CD8+ T cells to enable them to be used for adoptive cell transfer (ACT), a promising and rapidly developing immunotherapeutic approach to treat cancer which holds considerable potential as an therapeutic strategy to reconstitute the anti-viral immunity in immune-compromised patients to prevent their development of life-threatening viral infections. We demonstrated that the capacity of this IST platform to deliver TCR and CD28 signals to activate and generate large numbers of highly functional cytotoxic CD8+ T cells from the naïve repertoire specific for the melanoma-associated MART-1 antigen and the HIV-associated SL9 antigen. In contrast to naïve MART-1-specific CD8+ T cells which could be activated by both MART-1-peptide loaded dendritic cells and MART-1-specific IST, naïve SL-9-specific CD8+ T cells could be activated by SL9-specific IST but not by SL9-peptide loaded dendritic cells. This innovative approach has the potential to streamline the expansion of de novo antigen-specific T cells, overcoming the logistical hurdles limiting the wider use of ACT and enhancing its effectiveness as a therapeutic strategy for both cancer and HIV.

Graduate student and MSTP student authors are indicated by underlining

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