The study will be conducted in 3 parts. In Part 1, Dose Escalation, 2 sequentially enrolled cohorts of patients 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 eligible. In Part 2, 2 groups of patients 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, patients 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 patients with follicular NHL will be enrolled to receive local radiation therapy and intratumoral G100 (no tumor size requirement in this arm).