Downregulation of CD45 Signaling in COVID-19 Patients Is Reversed by C24D, a Novel CD45 Targeting Peptide.

Danny Alon,Cyrille J Cohen,Annat Raiter,Eyal Robinson,Julia Lipovetsky,Nirit Ganor,Yossi Paitan,Rinat Yerushalmi

doi:10.3389/fmed.2021.675963

Abstract

CD45, the predominant transmembrane tyrosine phosphatase in leukocytes, is required for the efficient induction of T cell receptor signaling and activation. We recently reported that the CD45-intracellular signals in peripheral blood mononuclear cells (PBMCs) of triple negative breast cancer (TNBC) patients are inhibited. We also reported that C24D, an immune modulating therapeutic peptide, binds to CD45 on immune-suppressed cells and resets the functionality of the immune system via the CD45 signaling pathway. Various studies have demonstrated that also viruses can interfere with the functions of CD45 and that patients with severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) are immune-suppressed. Given the similarity between the role of CD45 in viral immune suppression and our findings on TNBC, we hypothesized that the C24D peptide may have a similar “immune-resetting” effect on PBMCs from COVID-19 patients as it did on PBMCs from TNBC patients. We tested this hypothesis by comparing the CD45/TCR intracellular signaling in PBMCs from ten COVID-19 patients vs. PBMCs from ten healthy volunteers. Herein, we report our findings, demonstrating the immune reactivating effect of C24D via the phosphorylation of the tyrosine 505 and 394 in Lck, the tyrosine 493 in ZAP-70 and the tyrosine 172 in VAV-1 proteins in the CD45 signaling pathway. Despite the relatively small number of patients in this report, the results demonstrate that C24D rescued CD45 signaling. Given the central role played by CD45 in the immune system, we suggest CD45 as a potential therapeutic target.

Highlights

CD45 is a transmembrane protein tyrosine phosphatase receptor type C (PTPRC), expressed exclusively in leukocytes, with double opposing effects on T cell receptor (TCR) activity [1, 2]
Given the similarity between the CD45 viral immune suppression reported by others and our oncology findings, we hypothesized that the C24D peptide may have a similar immuneresetting effect on peripheral blood mononuclear cells (PBMCs) from COVID-19 patients as it did on PBMCs from triple negative breast cancer (TNBC) patients
We demonstrate in this Brief Report the effect of adding C24D to PBMCs obtained from ten hospitalized COVID-19 patients on the phosphorylation of lymphocyte-specific protein tyrosine kinase (Lck), Zeta-chain-associated protein kinase 70 (ZAP-70) and VAV-1 proteins in the CD45 signaling pathway

Summary

Introduction

CD45 is a transmembrane protein tyrosine phosphatase receptor type C (PTPRC), expressed exclusively in leukocytes, with double opposing effects on T cell receptor (TCR) activity [1, 2]. CD45 plays an inhibitory function involving the dephosphorylation of the tyrosine 394 (Y394) in the lymphocyte-specific protein tyrosine kinase (Lck), preventing its activation. CD45 plays the role of an activator when it dephosphorylates the tyrosine 505 (Y505), an inhibitory site at the C-terminal end of the non-receptor tyrosine-Src kinases. Activated Lck phosphorylates the immunoreceptor tyrosinebased activation motifs (ITAMs) of the T cell receptor (TCR)/CD3 complex. The phosphorylated ITAMs recruit the Zeta-chain-associated protein kinase 70 (ZAP-70), via its Src homology 2 (SH2) domains. For TCR activation, CD3bound ZAP-70 is activated by both Lck and (trans)-autophosphorylation at the ZAP70 tyrosine 493 (Y493) [3,4,5]. The ZAP70 tyrosine kinase transmits a downstream signal leading to VAV-1 phosphorylation and activation [6, 7]

Methods

Results

Conclusion