Study of Intratumoral G100 With Or Without Pembrolizumab or Rituximab In Participants With Follicular Non-Hodgkin's Lymphoma (MK-3475-174/IMDZ-G142)

This is a multi-center Phase 1/2 open label trial of intratumoral G100 in participants with low grade NHL. Eligible participants with NHL will be enrolled and receive G100 to an accessible tumor mass. Clinical response will be evaluated in the injected tumor and systemic (abscopal) responses will be evaluated in distal areas involved with tumor. The study will be conducted in 5 parts. In Part 1, Dose Escalation, 2 sequentially enrolled cohorts of participants will be treated at one of 2 dose levels of G100 using a standard escalation design. In this portion of the study, both follicular and marginal zone NHL will be eligible. In Part 2, 2 groups of participants with follicular NHL may be examined. One group will be randomly assigned to receive either single agent G100 intratumorally at the maximum safe dose determined in Part 1 following local radiation or will receive the same treatment regimen sequentially administered with pembrolizumab. A second treatment group may be explored if the safety profile in Part 1 is acceptable. In this optional group, participants with injectable tumors of 4 cm or greater would be enrolled and treated with a higher dose of G100. In Part 3, expansion of a higher dose (20µg of G100) in participants with follicular NHL will be enrolled to receive local radiation therapy and intratumoral G100. In Part 4, Dose Escalation and Expansion, a dose of 20µg of G100 will be examined as a treatment of 1 or more tumors (up to 4) with pembrolizumab in order to establish safety and examine clinical and biomarker responses in participants receiving increasing total systemic doses of G100 and Part 5, will evaluate standard induction therapy with rituximab (anti-CD20) in combination of escalating doses of intratumoral G100 in single tumors. The primary goal of this study is to determine the safety and tolerability of different doses of G100 when administered by intratumoral injection. The development of anti-tumor immune responses and preliminary evidence of clinical responses in local and distal tumor sites will also be examined.