Published in Molecular Cancer Therapeutics: Using Single-Cell Secretome to Understand How Immune Cells Respond to Cancer Therapy

The treatment of cutaneous T cell lymphoma (CTCL) has progressed to improve patient outcomes, although strategies to potentiate therapies are still being explored. Bexarotene, a retinoid X-receptor (RXR)-selective agonist, has been approved for the treatment of CTCL in patients who did not respond to at least one line of therapy. The binding of bexarotene and activation of RXR in CTCL cells leads to the transcription of genes associated with cell cycle arrest and apoptosis. However, systemic bexarotene also causes hypothyroidism in over 95% of patients, so levothyroxine, a medicine that acts as a replacement thyroid hormone, is routinely administered to counteract this adverse effect.

Thyroid hormones have numerous effects throughout the body - the interaction between the endocrine and immune system indicates that thyroid hormones are invaluable in maintaining proper immune function and response. However, in malignant T cells, certain thyroid hormones can increase cell proliferation and pro-cancer activity through integrin αVβ3 signaling.

The intricate interaction between immune cell function and thyroid signaling complicates current understanding of the roles of levothyroxine and bexarotene in CTCL; thyroid hormones may decrease the efficacy of bexarotene treatment, but a lack of thyroid hormones may decrease the anti-cancer activity of healthy lymphocytes. Furthermore, levothyroxine can activate integrin αVβ3, which is overexpressed on CTCL cells. Functional phenotyping of immune cells using IsoPlexis' single-cell technology can help researchers uncover the therapeutic mechanisms driving the immune cell treatment response.

Single-Cell Secretome Reveals Mechanism of Immune Response

In a study recently published in Molecular Cancer Therapeutics, researchers used IsoPlexis' Single-Cell Secretome to evaluate how monocytes react to bexarotene therapy. Preliminary RNAseq data showed that bexarotene increased IL-32 gene expression, which is associated with increased production of TNF-α, an inflammatory cytokine. Peripheral monocytes were compared before and after bexarotene treatment to characterize how the therapy affected cell function. The frequency of monocytes secreting TNF-α, IL-8, and IFN-γ were all increased after bexarotene treatment, indicating that bexarotene induces expression of immune genes and, subsequently, the production of cytokines in CTCL cells. Further experiments showed that this activity was dependent on levels of thyroid hormones and were in line with RNA sequencing data.

Additional studies assessed the effect of integrin αVβ3 inhibition on bexarotene therapy. Because normal lymphocytes do not express integrin αVβ3, inhibition could optimize bexarotene treatment while circumventing unwanted effects of levothyroxine treatment. By inhibiting integrin αVβ3, bexarotene therapy was more effective while levothyroxine was able to maintain immune activity. By using single-cell functional phenotyping to characterize immune cell response, the researchers were able to identify how bexarotene affects immune cells and help to inform strategies for attenuating off-target effects of bexarotene.

Single-Cell Functional Proteomics Unlocks Unique Insights

Single-cell functional analysis offers unique insights into heterogeneous cell populations. By characterizing immune function at the single-cell level, researchers can gain a better understanding of how individual cell secretions alter or drive immune response. This unique data layer helps to reveal mechanisms of treatment response, allowing researchers to refine therapies and improve patient outcomes.