A three-pronged treatment approach can produce responses in indolent non-Hodgkin lymphoma (iNHL), according to research published in Nature Medicine.
The approach – “in situ vaccination (ISV)” – involves intratumoral injections of Fms-like tyrosine kinase 3 ligand (Flt3L), local radiotherapy, and intratumoral injections of a TLR3 agonist (poly-ICLC).
ISV produced responses in patients with iNHL, prompting regression of tumors that were directly targeted with ISV, as well as untreated tumors.
In preclinical experiments, ISV induced tumor regression in mice but also overcame resistance to PD1 inhibition. This result led researchers to initiate atesting ISV in combination with pembrolizumab in patients with lymphoma and solid tumors.
“We discovered why some tumors do not respond to PD1 blockade: insufficient dendritic cells (DCs) and cross-presentation,” lead study author, of the Icahn School of Medicine at Mount Sinai, New York, said in an interview. “We developed a treatment, in situ vaccination (ISV), which brings DCs to the tumor, loads them with tumor antigens, and activates the DCs.”
Specifically, the researchers found that injecting Flt3L into a tumor recruits intratumoral DCs, local radiotherapy loads the DCs with tumor-associated antigens, and poly-ICLC activates DCs. This approach produced responses in mouse models of lymphoma and patients with iNHL.
Dr. Brody and his colleagues tested ISV in A20 tumor-bearing mice. The mice received intratumoral injections of Flt3L, followed by local radiotherapy and poly-ICLC.
Tumor regression occurred within days of radiotherapy. About 40% of mice experienced tumor-free survival of at least 3 months, although most tumors recurred within 4 weeks of ISV administration.
However, the researchers observed increased PD1 and PD-L1 expression in ISV-treated mice, so the team theorized that an anti-PD1 monoclonal antibody (RMP1-14) could improve the efficacy of ISV.
The researchers found that ISV plus RMP1-14 delayed tumor growth when compared with ISV alone, and the rate of durable remissions increased from about 40% to about 80%.
Dr. Brody and his colleagues also tested ISV in a clinical trial. Thatincluded 11 iNHL patients – 9 with follicular lymphoma, 1 with marginal zone lymphoma, and 1 with small lymphocytic lymphoma.
The patients received nine daily injections of Flt3L (25 mcg/kg) into a target lesion, then two doses of radiation (2 Gy) to the same lesion, and eight intratumoral injections of poly-ICLC (2 mg).
“We ... have observed dramatic clinical responses; i.e., we administer ISV at one tumor site, and tumors throughout the body regress,” Dr. Brody said.
At the target lesion, there were two complete responses, six partial responses, and three cases of stable disease. At nontarget lesions, there was one complete response, two partial responses, six cases of stable disease, and two cases of progression.
ISV was considered well tolerated. One patient had grade 2 fever, three had grade 1 fever, and nine had grade 1 flu-like symptoms. Two patients did not have any adverse events.
This research was supported by Merck, Celldex Therapeutics, Oncovir, and Genentech. The authors reported relationships with Acerta Pharma, Bristol Myers Squibb, Genentech, Gilead Sciences, Seattle Genetics, Pharmacyclics, Celgene, Celldex Therapeutics, and Oncovir.
SOURCE: Hammerich L et al. Nat Med. 2019 Apr 8.