Decade-Long Safety and Function of Retroviral-Modified Chimeric Antigen Receptor T Cells

Abstract

The success of adoptive T cell gene transfer for treatment of cancer and HIV is predicated on generating a response that is both durable and safe. Here we report long term results from three clinical trials to evaluate gammaretroviral vector engineered T-cells for HIV. The vector encoded a chimeric antigen receptor (CAR) comprised of CD4 linked to the CD3-ζ signaling chain (CD4ζ). CAR T-cells were detected in 98% of samples tested for at least 11 years post-infusion at frequencies that exceed average T cell levels after most vaccine approaches. The CD4ζ transgene retained expression and function. There was no evidence of vector-induced immortalization of cells as integration site distributions showed no evidence of persistent clonal expansion or enrichment for integration sites near genes implicated in growth control or transformation. The CD4ζ T cells have stable levels of engraftment, with decay half-lives that exceed 16 years, in marked contrast to previous trials testing engineered T cells. These findings indicate that host immunosuppression prior to T cell transfer is not required in order to achieve long term persistence of gene-modified T cells. Further, our results emphasize the safety of T cells modified by retroviral gene transfer in clinical application, as measured in >500 patient years of follow up. Thus, previous safety issues with integrating viral vectors are hematopoietic stem cell or transgene intrinsic, and not a general feature of retroviral vectors. Engineered T cells are a promising form of synthetic biology for long term delivery of protein based therapeutics. These results provide a framework to guide the therapy of a wide spectrum of human diseases.

Engineering HIV-Resistant, Anti-HIV Chimeric Antigen Receptor T Cells

“…8 In a randomized trial, this first-generation CAR was safe and reduced the HIV reservoir as measured by a viral outgrowth assay, and CAR + cells were detectable for 10 years despite the lack of clinical benefit. [30][31][32] The efficacy of this approach was likely compromised because of limited CAR activity in the absence of an intracellular co-stimulatory signaling domain and the potential for HIV infection of T cells expressing the CD4 CAR. 10,33 A panel of novel high-affinity, broadly neutralizing monoclonal antibodies (bNAbs) recognizing the HIV envelope glycoprotein have been isolated and characterized over the last decade.…”

HIV-1-Specific Chimeric Antigen Receptors Based on Broadly Neutralizing Antibodies

“…Unfortunately, this effort was abandoned after these trials showed safety but no clear benefits: one study with viremic subjects showed no reduction in viremia, although there appeared to be decreased rectal tissue virus burden (3), while another study of antiretroviral drug-treated subjects with baseline undetectable viremia not surprisingly showed no change in the persisting blood viral reservoir in the form of proviral DNA (4). Follow-up of these studies after more than a decade showed low-level persistence of transduced cells without evidence of malignancy (5).…”

The Flipside of the Power of Engineered T Cells: Observed and Potential Toxicities of Genetically Modified T Cells as Therapy

“…They found CAR T cell persistence in 98% of these patients for upward of 11 years without evidence of transformation. 47 Emphasizing their findings, of the >1,000 individuals who have been infused with CAR T cells to date, no documented transformational event has been observed.…”

“…46 In more than 500 patient-years of follow-up, no replication competent retrovirus has been identified. 47 Early replication-competent lentivirus could be generated in vitro by recombination of vector plasmids or in vivo by mobilization of vector DNA in the presence of other infectious lentivirus such as HIV. 44 Currently used self-inactivating lentiviral vectors generated from three-or four-plasmid transfections are substantially less susceptible to generation of recombinant virus; furthermore, transgene expression can be driven from a heterologous internal promoter, preventing in vivo recombination 48 and enhancing long-term stable expression.…”