CMV vector-vaccination – immunologic and virologic basis of CMV vaccine-induced protection

We have established that vaccination of Rhesus Macaques (RMs) with SIV insert-expressing 68-1 Rhesus Cytomegalovirus vectors (RhCMV) elicits an immune response that in 59% of vaccinees across multiple published studies can intercept and effectively arrest a primary, early spreading, and highly pathogenic SIV infection. This unique pattern of “replication arrest” efficacy has been linked to three 68-1 RhCMV/SIV immune characteristics, including the ability to generate and maintain: 1) high magnitude, circulating and tissue-based, effector memory-biased CD8⁺ T cell responses, 2) major histocompatibility complex (MHC)-E-restricted SIV-specific CD8⁺ T cell responses and 3) in RMs with MHC-E restricted CD8⁺ T cell responses, a protection-predictive innate immune transcriptional response to vaccination that includes a central IL-15 signaling component. However, the specific immune mechanisms underlying replication arrest protection are unknown. The major current focus of the lab is to elucidate the specific immune mechanisms underlying protection by extensively exploring each of these 3 specific attributes.   Currently, we are using sophisticated ‘omics technologies to enable detailed characterization of tissue immune responses to help define differences between vaccine modalities in vivo in the actual RM tissues hosting an early spreading SIV infection.  We are also seeking to define the minimal MHC-E-restricted CD8⁺ T cell receptor (TCR) recognition unit capable of mediating SIV replication arrest-type efficacy, asking the questions of whether efficacy requires recognition of one or multiple supertopes, and whether this efficacious recognition requires one or multiple TCR clonotypes.

CMV vaccines against Mycobacterium tuberculosis

Our lab has demonstrated that subcutaneous vaccination of RM with RhCMV vectors encoding Mtb antigen inserts (RhCMV/TB) reduces the overall (pulmonary and extra-pulmonary) extent of Mtb infection and disease by nearly 70% compared to unvaccinated controls, with intra-bronchial Erdman strain Mtb challenge occurring at ~1 year after first vaccination (Hansen 2018). We have found that complete vaccine-mediated immune control of highly pathogenic Mtb is possible if immune effector responses can intercept Mtb infection at its earliest stages and offer promise that a human CMV/TB vaccine might be effective in preventing pulmonary TB in adolescents and adults, and thereby contribute to ending the global TB epidemic. Based on these highly promising results, we, in collaboration with Vir Biotechnology, Inc. (Vir Bio), are moving a human CMV/TB vaccine into the developmental pipeline, while simultaneously confirming and extending our understanding of the immunobiology of RhCMV/TB vaccines in the RM-TB model. In 2019 we were awarded an NIH contract to help facilitate the rational design of an effective TB vaccine by identification of immune responses that are capable of controlling or eradicating Mtb. Understanding the unique immunobiology of the vector-elicited immune responses is critical to the overall goal of this program. The goal is to apply this information to define early immune events in the lung and draining lymph nodes that lead to Mtb eradication.

CMV vaccines against malaria

T cell targeted antigens presented by major histocompatibility complex (MHC) class I molecules on parasite-infected cells at any stage are largely unknown, a knowledge gap that has hampered the development of rationally designed, T cell- based vaccines for malaria. Malaria-specific CD8⁺ T cells have long been known to control the liver stages of malaria and we recently showed that they can also kill reticulocytes infected with Plasmodium vivax. Combining our understanding of MHC-E T cells with Dr. Brandon Wilder’s experience with the malaria parasite, we aim to determine the relative contribution of MHC-E in the presentation of P. vivax peptides to CD8⁺ T cells and investigate a possible role of MHC-E-targeting in CD8⁺ T cell killing of infected reticulocytes (iRetics). Following up on our 2019 paper, we are also comparing RhCMV-based P. vivax vaccines eliciting MHC-E or MHC-Ia-restricted responses to selected, conserved antigens with respect to their ability to protect against P. cynomolgi challenge in rhesus macaques.

CMV vaccines against influenza

To circumvent the problem of influenza sequence variability, in collaboration with Dr. Jonah Sacha, we are exploring whether a CMV-based vaccine that elicits and indefinitely maintains effector memory T cells (T_EM) at high frequency in the lung can protect against lethal influenza infection. To develop a CMV/Cynomolgus influenza model we have isolated Cynomolgus macaque CMV (CyCMV) and generated a strain which accurately emulates RhCMV in its ability to be programmed by genetic manipulation to elicit antigen-specific CD8⁺ T cell responses that are restricted by MHC-E-only, MHC-II-only and MHC-Ia-only in CM.  We are currently in the process of testing whether this potent new type of cellular immunity can protect from influenza virus infection.

CMV vectors for cancer

We have identified several MHC-E restricted SIV-specific TCRs that recognize both RM and human MHC-E. In collaboration with Dr. Klaus Früh, we immunized RM with 68-1 RhCMV-vectors expressing prostatic acidic phosphatase (PAP), Wilms tumor-1 (WT-1) protein or mesothelin.  Remarkably, T cell responses to all three tumor antigens were comparable to viral antigen-specific responses in frequency, duration, phenotype, epitope density and MHC-restriction. Since these tumor antigens are known to be expressed in healthy tissue, this result suggests that CMV vectored cancer vaccines can overcome immunological tolerance. We further demonstrate that PAP-specific, MHC-E-restricted CD8⁺ T cells from RhCMV/PAP-immunized RM are stimulated by PAP-expressing cancer cell lines and cancer cells, indicating that cancer cells are able to present tumor antigen-derived peptides via MHC-E. These results suggest that the HLA-E/NKG2A immune checkpoint can be exploited for T cell-based immunotherapies.

CMV vectors for Chronic Hepatitis B Virus

We are collaborating with Dr. Ben Burwitz to evaluate whether HBV-specific CD8+ T cells restricted by MHC-E would be an effective therapeutic for suppressing HBV infections.  Utilizing the NHP model, we are currently vaccinating animals with 68-1/miR-126-based vectors expressing HBV antigens, with the goal of eliciting HBV-specific MHC-E-restricted CD8⁺ T cells and identifying the immunodominant epitopes. If this proves successful, we will characterize the T cell receptors (TCRs) of these MHC-E-restricted CD8⁺ T cells with the goal of using these TCRs to recognize and suppress HBV infection as a possible therapeutic strategy against CHB. 

HCMV Vaccine Platform (Phase 1b Clinical Trial)

The CMV-vector platform is currently being evaluated in a Phase 1b first-in-human (FIH), multiple-site, double-blind, placebo-controlled study in healthy adult volunteers 18 to 50 years of age who are CMV seropositive and HIV uninfected. The industry sponsored study is designed as a 3-cohort dose escalation. My laboratory is a designated secondary scientific site with the main objective of characterizing the immunogenicity of the vaccine as measured by insert-specific (HIV-1 Gag antigen) CD4+ and CD8+ T cell response magnitude, function, and phenotypic profile using intracellular cytokine staining (ICS) and flow cytometry techniques.

Other on-going clinical studies

In May of 2021, Dr. Hansen’s Human Samples Laboratory (HSL) was asked by an industry sponsor to intake samples from several ongoing clinical studies involving HIV, NASH and COVID-19 long haulers. Data we have generate has been used in 3 manuscripts (one published, one currently in review, and one in preparation) and 3 abstracts for presentations at international meetings, including American Association for the Study of Liver Diseases (AASLD) and the European Association for the Study of the Liver (EASL).  Our biomarker research has greatly expanded the sponsor’s understanding on the mechanism of action of their proprietary compound.