Gita Chu Abhiraman

All Publications

• Overcoming lung cancer immunotherapy resistance by combining non-toxic variants of IL-12 and IL-2. JCI insight Horton, B. L., D'Souza, A. D., Zagorulya, M., McCreery, C. V., Abhiraman, G. C., Picton, L. K., Sheen, A., Agarwal, Y., Momin, N., Wittrup, K. D., White, F. M., Garcia, K. C., Spranger, S. 2023

  Abstract

  Engineered cytokine-based approaches for immunotherapy of cancer are poised to enter the clinic, with IL-12 being at the forefront. However, little is known about potential mechanisms of resistance to cytokine therapies. We found that orthotopic murine lung tumors were resistant to systemically delivered IL-12 fused to murine serum albumin (MSA, IL12-MSA) due to low IL-12R expression on tumor-reactive CD8+ T cells. IL2-MSA increased binding of IL12-MSA by tumor-reactive CD8+ T cells, and combined administration of IL12-MSA and IL2-MSA led to enhanced tumor-reactive CD8+ T cell effector differentiation, decreased numbers of tumor-infiltrating CD4+ regulatory T (Treg) cells, and increased survival of lung tumor-bearing mice. Predictably, the combination of IL-2 and IL-12 at therapeutic doses led to significant dose-limiting toxicity. Administering IL-12 and IL-2 analogs with preferential binding to cells expressing IL12rb1 and CD25, respectively, led to a significant extension of survival in mice with lung tumors while abrogating dose-limiting toxicity. These findings suggest that IL-12 and IL-2 represent a rational approach to combination cytokine therapy whose dose-limiting toxicity can be overcome with engineered cytokine variants.

  View details for DOI 10.1172/jci.insight.172728

  View details for PubMedID 37669107

• A structural blueprint for interleukin-21 signal modulation. Cell reports Abhiraman, G. C., Bruun, T. U., Caveney, N. A., Su, L. L., Saxton, R. A., Yin, Q., Tang, S., Davis, M. M., Jude, K. M., Garcia, K. C. 2023; 42 (6): 112657

  Abstract

  Interleukin-21 (IL-21) plays a critical role in generating immunological memory by promoting the germinal center reaction, yet clinical use of IL-21 remains challenging because of its pleiotropy and association with autoimmune disease. To better understand the structural basis of IL-21 signaling, we determine the structure of the IL-21-IL-21R-γc ternary signaling complex by X-ray crystallography and a structure of a dimer of trimeric complexes using cryo-electron microscopy. Guided by the structure, we design analogs of IL-21 by introducing substitutions to the IL-21-γc interface. These IL-21 analogs act as partial agonists that modulate downstream activation of pS6, pSTAT3, and pSTAT1. These analogs exhibit differential activity on T and B cell subsets and modulate antibody production in human tonsil organoids. These results clarify the structural basis of IL-21 signaling and offer a potential strategy for tunable manipulation of humoral immunity.

  View details for DOI 10.1016/j.celrep.2023.112657

  View details for PubMedID 37339051

• Structure-based decoupling of the pro- and anti-inflammatory functions of interleukin-10. Science (New York, N.Y.) Saxton, R. A., Tsutsumi, N., Su, L. L., Abhiraman, G. C., Mohan, K., Henneberg, L. T., Aduri, N. G., Gati, C., Garcia, K. C. 2021; 371 (6535)

  Abstract

  Interleukin-10 (IL-10) is an immunoregulatory cytokine with both anti-inflammatory and immunostimulatory properties and is frequently dysregulated in disease. We used a structure-based approach to deconvolute IL-10 pleiotropy by determining the structure of the IL-10 receptor (IL-10R) complex by cryo-electron microscopy at a resolution of 3.5 angstroms. The hexameric structure shows how IL-10 and IL-10Ralpha form a composite surface to engage the shared signaling receptor IL-10Rbeta, enabling the design of partial agonists. IL-10 variants with a range of IL-10Rbeta binding strengths uncovered substantial differences in response thresholds across immune cell populations, providing a means of manipulating IL-10 cell type selectivity. Some variants displayed myeloid-biased activity by suppressing macrophage activation without stimulating inflammatory CD8+ T cells, thereby uncoupling the major opposing functions of IL-10. These results provide a mechanistic blueprint for tuning the pleiotropic actions of IL-10.

  View details for DOI 10.1126/science.abc8433

  View details for PubMedID 33737461

• Generation of Ca2+-independent sortase A mutants with enhanced activity for protein and cell surface labeling PLOS ONE Jeong, H., Abhiraman, G. C., Story, C. M., Ingram, J. R., Dougan, S. K. 2017; 12 (12): e0189068

  Abstract

  Sortase A, a calcium-dependent transpeptidase derived from Staphylococcus aureus, is used in a broad range of applications, such as the conjugation of fluorescent dyes and other moieties to proteins or to the surface of eukaryotic cells. In vivo and cell-based applications of sortase have been somewhat limited by the large range of calcium concentrations, as well as by the often transient nature of protein-protein interactions in living systems. In order to use sortase A for cell labeling applications, we generated a new sortase A variant by combining multiple mutations to yield an enzyme that was both calcium-independent and highly active. This variant has enhanced activity for both N- and C-terminal labeling, as well as for cell surface modification under physiological conditions.

  View details for DOI 10.1371/journal.pone.0189068

  View details for Web of Science ID 000417033200027

  View details for PubMedID 29200433

  View details for PubMedCentralID PMC5714338