DNA mismatch repair proficient (pMMR) metastatic colorectal cancer (mCRC) is not responsive to pembrolizumab monotherapy. DNA methyltransferase inhibitors can promote antitumor immune responses. This clinical trial investigated whether concurrent treatment with azacitidine enhances the antitumor activity of pembrolizumab in mCRC.

We have conducted a phase 1 study of intravenous vvDD, a Western Reserve strain oncolytic vaccinia virus, on 11 patients with standard treatment-refractory advanced colorectal or other solid cancers. The primary endpoints were maximum tolerated dose and associated toxicity while secondary endpoints were pharmacokinetics, pharmacodynamics, immune responses, and antitumor activity. No dose-limiting toxicities and treatment related severe adverse events were observed. The most common adverse events were grades 1/2 flu-like symptoms. Virus genomes were detectable in the blood 15-30 minutes after virus administration in a dose-dependent manner. There was evidence of a prolonged virus replication in tumor tissues in two patients, but no evidence of virus replication in non-tumor tissues, except a healed injury site and an oral thrush. Over 100-fold of anti-viral antibodies were induced in patients' sera. A strong induction of inflammatory and Th1, but not Th2 cytokines, suggested a potent Th1-mediated immunity against the virus and possibly the cancer. One patient showed a mixed response on PET-CT with resolution of some liver metastases, and another patient with cutaneous melanoma demonstrated clinical regression of some lesions. Given the confirmed safety, further trials evaluating intravenous vvDD in combination with therapeutic transgenes, immune checkpoint blockade or complement inhibitors, are warranted.

Regulatory T cells (Tregs) are a barrier to anti-tumor immunity. Neuropilin-1 (Nrp1) is required to maintain intratumoral Treg stability and function but is dispensable for peripheral immune tolerance. Treg-restricted Nrp1 deletion results in profound tumor resistance due to Treg functional fragility. Thus, identifying the basis for Nrp1 dependency and the key drivers of Treg fragility could help to improve immunotherapy for human cancer. We show that a high percentage of intratumoral NRP1+ Tregs correlates with poor prognosis in melanoma and head and neck squamous cell carcinoma. Using a mouse model of melanoma where Nrp1-deficient (Nrp1-/-) and wild-type (Nrp1+/+) Tregs can be assessed in a competitive environment, we find that a high proportion of intratumoral Nrp1-/- Tregs produce interferon-γ (IFNγ), which drives the fragility of surrounding wild-type Tregs, boosts anti-tumor immunity, and facilitates tumor clearance. We also show that IFNγ-induced Treg fragility is required for response to anti-PD1, suggesting that cancer therapies promoting Treg fragility may be efficacious.

E1697 was a phase III trial of adjuvant interferon (IFN)-α2b for one month (Arm B) versus observation (Arm A) in patients with resected melanoma at intermediate risk. We evaluated the levels of candidate serum cytokines, the HLA genotype, polymorphisms of CTLA4 and FOXP3 genes and the development of autoantibodies for their association with relapse free survival (RFS) in Arm A and Arm B among 268 patients with banked biospecimens.