My research program has three major areas of focus: (1) oncolytic virotherapy, (2) investigating novel immune checkpoint ligands and receptors, and (3) developing/advancing single vector CRISPR/HDR technology.
1) Oncolytic Virotherapy
In collaboration with other University of Utah and Huntsman Cancer institute clinicians we are investigating biomarkers of response from ongoing clinical trials evaluating investigational oncolytic viruses in combination with immune checkpoint inhibitors in patients with advanced melanoma. The goal is to identify and understand differences in responses in order to develop better treatment strategies. We have developed several novel tumor selective oncolytic Picornaviruses in my lab that we are currently evaluating in preclinical melanoma models. Each utilizes a distinct cellular receptor (frequently expressed on tumor cells) for entry and elicits unique replication and lytic programs. We have observed significant antitumor activity in human melanoma, glioblastoma, pancreatic and breast cancer cell lines along with patient derived multiple myeloma cells. Importantly, these viruses have very limited capacity to infect normal host cells, despite expression of viral receptors, due to intact innate immunity. The transition from a normal cell to cancer necessitates loss of one or more innate immune pathways that also makes cancerous cells susceptible to productive viral infection. The variability we see in viral lytic cell death between cancer cells is more reflective of the number of impaired innate pathways than receptor density. The ultimate goal is to advance these oncolytic viruses and strategies for viral persistence into clinical trials as single agents and in combination with immune checkpoint blockade.
2) B7-H3 (CD276)
B7 family members are normally expressed on antigen presenting cells and provide co-stimulatory and suppressive signals that regulate T-cell activation/response, thereby promoting a sufficient immune response to pathogens while limiting host response. The best characterized members are B7 (binds to CTLA4 to suppress T-cell activation) and PD-L1 (B7-H1, binds to PD-1 receptor on T-cells and blockade enhances T-cell activation). Recently, additional B7 family ligand members have been identified including CD276 (B7-H3). B7-H3 shares 20-27% identity with other B7 members and four major transcripts have been identified including a soluble form. Tumor expression of B7-H3 and expression of soluble B7-H3 has been associated with a poor prognosis in melanoma, breast, prostate, lung adenocarcinoma, colorectal, gliomas, and pancreatic cancer while the receptor for B7-H3 remains unknown. B7-H3 is an emerging immunotherapeutic target and several anti-B7-H3 strategies have been evaluated clinically, including CAR T cells and antibody (non-blocking, ADCC inducing) mediated tumor cell targeting strategies. Each of these approaches exploits high B7-H3 expression on tumor cells for selective targeting. We evaluated a role for B7-H3 in immune evasion in an immune competent murine melanoma model and observed a significant reduction in tumor take rates following CRISPR mediated loss of B7-H3 in an orthotopic transplant model further highlighting B7-H3 as a therapeutic target. We are currently attempting to identify the cellular receptor for this immune checkpoint ligand and are generating antibodies that may block B7-H3 from binding to its receptor, thereby blocking a negative signal that may ultimately enhance host antitumor immunity analogous, yet distinct from PD-1 and CTLA-4 blockade.
3) Single vector CRISPR/HDR
We have developed a novel method for single vector CRISPR mediated homology directed repair (HDR) that has high potential in developing novel relevant disease/cancer models and gene therapy applications. As proof of principle, we evaluated the ability of our CRISPR/Cas9-HDR viral vector to correct altered GFP (possessing an early termination codon) in vitro. We observed a 23% repair rate with our single vector design comparable to current state of the art ssDNA oligo (17.7%). We have also observed similar results with another CRISPR nuclease hAsCpf1 (15%) and are currently evaluating the much smaller CjCas9 in this model. The real advantage of this novel design is in vivo application as it involves delivery of a single adenoviral vector rather than multiple components in order to generate a precise genomic alteration. The highest reported single locus efficiency with multiple components is less than 0.1% in vivo. We are evaluating the ability of our single CRISPR/HDR strategy in several reporter and monogenic disease models including CFTR (ΔF508) and the much more difficult DMD (exon 45, exons 2-5, exons 45-50) alterations to see what kind of corrective efficiency we can achieve and its impact. If preclinical data is promising our long term goal is clinical evaluation as presently there are no cures for these genetic disorders.