IL-21 is a cytokine that activates STAT3, a master transcription factor involved in a broad spectrum of adaptive and innate immune functions.

In oncology, IL-21 has historically demonstrated promising signs of efficacy in early clinical studies, but was hindered by toxicities and pleiotropic effects, such as suppression of antigen presentation, which could dampen overall anti-tumor efficacy. Similar to the concept behind AB248, our cis-targeted IL-2, we hypothesized that focusing the activity of IL-21 to only the immune cell type primarily responsible for anti-tumor efficacy, while avoiding activation of other cells, would maximize the efficacy potential of IL-21 and reduce toxicity.We have developed a cis-targeted IL-21 activating cytokine that selectively targets CD8+ T cells, the immune cell type driving anti-tumor response. The IL-21 activating cytokine promotes cytotoxicity, memory cell differentiation, survival and reinvigoration of CD8+ T cells, all of which support anti-tumor activity.

We believe that CD8-IL21 cytokine has the potential to treat tumor types that may not be responsive to IL-2 and/or PD-1 therapy. PD-1-resistant tumors are associated with reduced memory T cell numbers and increased exhausted T cell numbers, suggesting that this molecule may be beneficial in these resistant tumors. CD8-IL-21 also has the potential to be used in combination with AB248 to enhance efficacy by combining a proliferation signal with one that optimizes functionality and prevents T cell exhaustion.



AB821 is >1000x selective for CD8+ T Cells


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