An immunotherapy antibody targeting CD4 T-cells anergy in HIV and cancer
CD4 T lymphocytes are immune cells whose activation is crucial in immune responses to promote and regulate the functions of other cells, including monocytes, macrophages, NK cells[1, 2, 3], B lymphocytes  and cytotoxic CD8 T cells . However, CD4 T cells can also become inactive while remaining alive , acquiring a status termed anergy, in which they proliferate less and produce less cytokines (the molecular messengers used to communicate with other immune cells). CD4 T cell anergy is a physiological phenomenon that plays a role in establishing tolerance to markers of self and prevents auto-immune responses .
In addition, CD4 T cell anergy also occurs in pathological conditions, preventing necessary immune responses and therefore contributing to the establishment of chronic diseases associated with immune deficiencies. Sometimes accompanied by CD4 T cell depletion, anergy has been observed in several infectious contexts, including bacterial [8, 9, 10], viral [11, 12, 13, 14, 15] and parasitic infections . Anergic CD4 T cells have also been observed in a number of solid and blood cancers arguing that their unresponsive state may hinder the establishment of an efficient anti-tumor immune response [17: Colorectal cancer, Metastatic cancers, Review T cell anergy, Pancreatic cancer]. Reverting the anergic status of CD4 T cells has therefore emerged as an attractive therapeutic means to restore functional immunity in these pathological contexts.
Diaccurate is developing a sole-in-class immunotherapy antibody that blocks the pathogenic activity of PLA2G1B, a blood soluble enzyme involved in CD4 T cell anergy in HIV-infected patients. DIACC1010 is currently in early preclinical development in HIV and discovery stage in oncology.
Understanding CD4 T cell anergy in HIV-infected patients
The immune deficiency that characterizes most HIV-infected patients is intimately linked to dysfunctional CD4 T lymphocytes. Fewer than 10% of circulating CD4 T cells are effectively infected by the virus  and yet the overall numbers of these cells progressively decline and the remaining cells display profound functional defects . Over the years, research by Prof. Jacques Thèze and colleagues has largely contributed to characterizing these CD4 T cell dysfunctions. In particular, they demonstrated that the cells became unresponsive to stimulation by the IL-7 cytokine [20, 21, 22], resulting in failure to activate the intracellular signaling pathway JAK/STAT [23, 24, 25]. But the mechanism that originally caused CD4 T cells to become anergic had long remained unknown.
In a study published by Pr. Thèze’s group in 2020, the scientists examined dysfunctional CD4 T cells by stimulated emission depletion microscopy and showed that over 80% of resting cells from viremic patients (VP) had a “bumpy” appearance owing to the presence of abnormally large membrane microdomains at their surface (aMMDs). This unusual morphological feature was absent from CD4 T cells in healthy donors (HD) . Upon stimulation with IL-7, bumpy CD4 T cells from VP remained morphologically unchanged and unresponsive. In contrast, HD CD4 T cells rearranged their membrane to display small, physiological membrane microdomains (pMMDs) and responded with activation of the JAK/STAT pathway. Importantly, the receptors of the IL-7 cytokine (IL-7R) were found to become trapped in the aMMDs of CD4 T cells from VP, providing evidence that their functional defects were due to their membrane abnormalities.
The researchers then found that these cellular defects were caused by a circulating enzyme, phospholipase PLA2G1B. In vivo, they showed that PLA2G1B acts in conjunction with a viral protein, gp41, that possibly targets the phospholipase to the surface of CD4 T lymphocytes, where the enzyme digests the lipids that form the cell membrane and causes the membrane defects (Figure 1). The gp41 viral protein acts therefore as a cofactor amplifying the digestion of the membrane by PLA2G1B. Interestingly, a similar mechanism was observed in presence of large amount of enzyme PLA2G1B with or without presence of a gp41 cofactor.
The anti-PLA2G1B antibody should reverse CD4 T cell dysfunctions
To counter the effects of PLA2G1B on CD4 T cells, the researchers developed a mouse monoclonal antibody (mAb) that inhibits the enzymatic activity of the protein. In vitro, the anti-PLA2G1B mAb suppresses PLA2G1B-induced CD4 T cell death and restores CD4 T cell response to cytokine stimulation by IL-7. In vivo, the antibody suppresses the unresponsiveness of CD4 T cells induced by human PLA2G1B injection in mice. Upon humanization, an anti-PLA2G1B mAb named DIACC1010 retained the ability to restore CD4 T cell response to IL-7, becoming a promising immunotherapeutic tool to reverse CD4 anergy in HIV patients, by inhibiting the action of PLA2G1B (Figure 1).
The current treatment of HIV-infected patients consists of antiretroviral therapy (ART), a combination of antiviral drugs that leads to full recovery of CD4 T cell numbers and function in 80% of patients, who display a near to normal life expectancy. However, up to 20% of HIV patients under ART present persistently low counts of CD4 T lymphocytes and are at higher risk of developing other diseases, including cancer. DIACC1010 is a promising treatment, complementary to ART, that could restore CD4 repertoire and function in these patients.
Figure 1: mechanism of action of DIACC1010
Healthy CD4 T cells form physiological membrane microdomains (pMMDs) upon activation with IL-7 and respond by activating JAK/STAT5 signaling. In the presence of pathogen, the PLA2G1B phospholipase acts in concert with a pathogenic peptide (the gp41 cofactor in HIV-infected patients) to induce the formation of abnormal membrane microdomains (aMMDs) which trap surface proteins such as the IL-7 receptor (IL-7R) and block their function. The resulting “bumpy CD4 T cells” become anergic and fail to activate the JAK/STAT5 pathway in response to IL-7 stimulation. A similar mechanism has been observed in presence of large amount of enzyme without presence of a cofactor. Treatment of HIV patients with the anti-PLA2G1B mAb DIACC1010 is expected to block the action of PLA2G1B and restore functionality of CD4 T cells.
DIACC1010 in other pathological contexts and cancers
CD4 T cell anergy has also been observed in other diseases, including cancer. Among other malignancies, CD4 T cell dysfunction was already thought to play an important role in immune evasion of pancreatic cancer cells . In addition, searching for peptides that could act as PLA2G1B cofactors, like gp41 in the case of HIV, Diaccurate scientists found a peptide derived from Porphyromonas gingivalis, an oral pathogen whose presence is highly associated with an increased risk of pancreatic cancer . The researchers then found that plasma from pancreatic cancer patients could render CD4 T cells unresponsive to IL-7 stimulation, an effect that was suppressed using an anti-PLA2G1B mAb. These findings indicate that CD4 T cell activity can be restored in cancer, and support the development of DIACC1010 for the treatment of pancreatic cancer to reestablish active CD4 T cells.
Preclinical studies to characterize DIACC1010 immunopharmacological functions in HIV are currently under way. The company intends to establish a partnership with a leader in the field to confirm the potential of the anti-PLA2G1B immunotherapy mAb in SHIV models (the gold standard for preclinical development in HIV) then in HIV-infected patients.
In 2021, Diaccurate initiated a research program in oncology to validate cancer co-factors, assess PLA2G1B expression profile in different tumors and develop various tools such as surrogate anti-mouse PLA2G1B antibody and mouse models. The objective is to establish an actionable preclinical Proof-of-Concept of DIACC1010 in solid tumors in 2022 and initiate human clinical trials by 2024.
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