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 Phase 1/2 open label trial of G100 in participants with low grade Non-Hodgkin's Lymphoma (NHL). G100 is composed of glucopranosyl lipid A in a stable emulsion and is a potent TLR4 (toll-like receptor-4) agonist. G100 will be administered by direct injection (intratumorally) into tumors of low grade NHL with or without standard low dose radiation therapy. Preclinical models and clinical studies in other cancers such as Merkel cell carcinoma have demonstrated that G100 administered in this manner can alter the tumor microenvironment, activate dendritic cells, T cells and other immune cells and induce systemic anti-tumor immune responses. In this trial, the safety, immunogenicity, and preliminary clinical efficacy of G100 will be examined alone or with pembrolizumab.

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.

Eligibility Criteria:
Inclusion Criteria:

1. Follicular low-grade NHL:

   * In Part 1-3: either treatment naïve (except for France) OR relapsed or refractory following at least one prior treatment.
   * In Part 4, enrollment is limited to relapsed OR refractory follicular NHL participants.
   * In Part 5, enrollment will include relapsed and refractory CD20+ follicular NHL following at least one but not more than 2 prior treatments.
2. Tumor mass(es) accessible for intratumoral injection

   * For Part 1-3, are being considered for local radiation therapy and at least one additional site of disease outside the radiation field for assessment of distal (abscopal) response.
   * For Part 4 and 5, radiation therapy is omitted. Measurable tumor mass(es) accessible for intratumoral injection must be present for treatment and assessment of response.
3. ≥ 18 years of age
4. Life expectancy of ≥ 6 months per the investigator
5. Eastern Cooperative Oncology Group (ECOG) performance status of 0 or 1
6. Electrocardiogram (ECG) without evidence of clinically significant arrhythmia or ischemia
7. If female of childbearing potential (FCBP), willing to undergo pregnancy testing and agrees to use two methods of birth control or is considered highly unlikely to conceive during the dosing period and for three months after last study treatment, or if receiving pembrolizumab, four months after last treatment
8. If male and sexually active with a FCBP, must agree to use highly effective contraception such as latex condom or is sterile (e.g. following a surgical procedure) during the dosing period and for three months after last study treatment, or if receiving pembrolizumab, four months after last treatment

Exclusion Criteria:

1. Cancer therapies, including chemotherapy, radiation (non-study regimen related), biologics or kinase inhibitors, granulocyte-colony stimulating factor (G-CSF) or granulocyte/monocyte-colony stimulating factor (GM-CSF) within 4 weeks prior to the first scheduled G100 dose
2. Investigational therapy within 4 weeks prior to G100 dosing
3. Prior administration of other intratumoral immunotherapeutics
4. Inadequate organ function including:

   1. Marrow: Peripheral blood leukocyte count (WBC) \< 3000/mm\^3, absolute neutrophil count ≤ 1500/mm\^3, platelets \< 75000/mm\^3, or hemoglobin \< 10 gm/dL
   2. Hepatic: alanine aminotransferase (ALT), and aspartate aminotransferase (AST) \> 2.5 x Upper Limit of Normal (ULN), total serum bilirubin \> 1.5 x ULN (participants with Gilbert's Disease may be included if their total bilirubin is ≤3.0 mg/dL)
   3. Renal: Creatinine \> 1.5x ULN
   4. Other: INR (international normalized ratio) or partial thromboplastin time (PTT) \>1.5 x ULN
5. Significant immunosuppression from:

   1. Concurrent, recent (≤ 4 weeks ago) or anticipated treatment with systemic corticosteroids at any dose, or
   2. Other immunosuppressive medications such as methotrexate, cyclosporine, azathioprine or conditions such as common variable hypogammaglobulinemia
6. Pregnant or nursing
7. Myocardial infarction within 6 months of study initiation, active cardiac ischemia or New York Heart Association (NYHA) Grade III or IV heart failure
8. History of other cancer within 2 years (except non-melanoma cutaneous malignancies and cervical carcinoma in situ)
9. Recent (\<1 week ago) clinically significant infection, active tuberculosis or evidence of active hepatitis B, hepatitis C or HIV infection
10. Central nervous system involvement with lymphoma, including parenchymal and leptomeningeal disease.
11. Significant autoimmune disease, including active non-infectious pneumonitis, with the exception of alopecia, vitiligo, hypothyroidism or other conditions that have never been clinically active or were transient and have completely resolved and require no ongoing therapy
12. Psychiatric, other medical illness or other condition that in the opinion of the principal investigator (PI) prevents compliance with study procedures or ability to provide valid informed consent
13. History of significant adverse or allergic reaction to any component of G100 and, if enrolled in Part 2 or Part 4, pembrolizumab and/or any of its excipients, and if enrolled in Part 5, anti-CD20 antibodies including rituximab and/or any of its excipients
14. Use of anti-coagulant agents or history a significant bleeding diathesis. (If a superficial lymph node or subcutaneous mass is to be injected, participants on agents such as non-steroidal anti-inflammatory drugs (NSAIDs), aspirin, or clopidogrel are eligible and these agents do not have to be withheld. For procedures with moderate or significant risk of bleeding, long-acting agents such as aspirin or clopidogrel should be discussed with the Medical Monitor and may need to be discontinued before G100 therapy.

    For participants enrolled in Part 2 or Part 4 with the potential to receive pembrolizumab:
15. History of (non-infectious) pneumonitis that required steroids or has current pneumonitis or interstitial lung disease
16. Received a live virus vaccine within 30 days of planned study start
17. Has undergone prior allogeneic hematopoietic stem cell transplantation within the last 5 years. (Participants who have had a transplant greater than 5 years ago are eligible as long as there are no symptoms of graft vs. host disease \[GVHD\]).
18. Has had an allogeneic tissue/solid organ transplant
19. Has received prior therapy with an anti-PD-1, anti-programmed death ligand (PD-L)1, or anti-PD-L2 agent or if the participant has previously participated in Merck MK-3475 clinical trials or was previously treated with an agent directed to another stimulatory or co-inhibitory T-cell receptor (e.g., CTLA-4, OX 40, CD137) and was discontinued from that treatment due to a Grade 3 or higher immune-related adverse event.