This multicenter phase 1/2 clinical trial evaluated intratumoral SD-101, a TLR9 agonist, and low-dose radiation in patients with untreated indolent lymphoma. 29 enrolled patients received 4 Gy of radiation followed by five weekly intratumoral injections of SD-101 at a single tumor site. No treatment-related grade 4 or serious adverse events occurred. Nearly all patients had tumor reduction at their treated site. More importantly, 24 patients had tumor reduction at their non-treated sites with 5 patients achieving a partial response and one achieving a complete response. Treatment-related increases of CD8+ and CD4+ effector T-cells and decreases of T Follicular Helper and T regulatory cells (Tregs) were observed in the tumor microenvironment. Low pre-treatment levels of CD4+ Tregs, proliferating CD8+ T-cells, and GranzymeB+ CD8+ T-cells were associated with favorable outcomes. Intratumoral SD-101 in combination with low-dose radiation is well tolerated and results in regression of both treated and untreated sites of disease.
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