The current pandemic driven by SARS-CoV2 creating the COVID-19 disease state is creating enormous healthcare challenges globally with limited treatment paradigms outside of supportive medical, and intensive care measures.
As the human population was entirely naïve to this viral pathogen, a particularly vigorous response of the immune cascade through cell-mediated mechanisms is a driving force behind the lethality of this disease in susceptible individuals. It is not presently understood why specific populations are at higher risk for disease state progression outside of traditional parameters such as age and pre-existing co-morbid health states. Furthermore, we lack a priori ways of identifying which SARS-COv2 infected patient may ultimately develop a "hyperactive" immune response that leads to the "cytokine storm" or "cytokine release syndrome", and the resultant cell, tissue, and organ system dysfunction.(1) Hypotheses in this area may include viral load phenomenon, aberration in immune/inflammatory regulatory check-points (JAK-STAT, JNK etc.), or underlying case dependent genetic factors (HLA etc.) influencing the immune system (2). Once the cytokine storm drives the clinical endpoint above, an affected patient who survives will become high risk for secondary pathogenic infection.
Intravenous remdesivir (3) along with dexamethasone (4, 5) have become standard of care therapeutics. The FDA recently provided emergency use authorization (EUA) for a novel SARS-COV2 neutralizing monoclonal antibody cocktail targeting the spike protein that docks with the ACE2 receptor on susceptible cells (Regeneron) (5). Rapid development of robust viral treatment strategies and vaccine development are the key strategies to managing SARS-COV2 in the long term. To this end, the FDA will be reviewing an EUA application for Pfizer's mRNA vaccine in early December, with similar review expected for Moderna's mRNA vaccine.
However, promising these developments are, thousands of patients are dying from cytokine storm mediated endpoints on a daily basis in the United States and across the world during the ongoing third wave/surge of COVID-19. There is broad recognition of this cytokine phenomenon, and in this era of targeted interleukin therapy for autoimmune disease states, a multitude of FDA approved monoclonal antibodies targeted to specific interleukins exist. Many institutions adopted IL-6 as a target for mitigation of the cytokine storm, and are utilizing tocilizumab (Actemra ®, Roche/Genentech) as a treatment (6) Sarilumab (Kevzara ®, Sanofi/Regeneron), another monoclonal Ab to IL-6, underwent rapid assessment for use in COVID-19(7). Both therapeutics did not meet primary specified endpoints in broader, Phase 2-3 studies.
These studies targeted the Th2/Tfh cytokine IL-6, as it plays a role in cytokine mediated inflammation in the lungs (9, 10) There is evidence that Il-6 can be induced within several hours by certain viral species (11) perhaps providing another reason why this was chosen as a target. Finally, this cytokine may serve as a target based on existing protocols to treat macrophage activation syndrome (MAS), and based on early evidence of cytokine expression patterns in patients infected with SARS-COV2 in Wuhan, PRC (2, 12-14). Classically, however, Th2/Tfh related cytokines are associated with antibody mediated immune memory and response, and though Th2/Tfh cytokines play a crucial role in acute inflammation, we have not seen protocols that target differentiating cytokines that drive Th0 to Th1 maturation, or Th1 specific cytokines. The Th1 cytokine profile is more consistently demonstrated in almost all early viral infection, and therefore, we view these cytokines as potential targets for therapy to prevent or mitigate the cytokine storm (Figure 1) (2, 12). Cytokine storm is a downstream manifestation of the viral induced host response that represents either failure of the initial host response to mitigate viral load, an uncontrolled late cytotoxic T-cell activity, or both. There is no evidence that targeted therapy against Th1 cytokines impairs the host response with strong clinical evidence supporting use in other EBV mediated secondary HLH syndromes (15).
The cytokine environment in which antigen primed T cells differentiate determines the subset that develops. In particular, IL-4 is essential for the development of Th2 response and IFN-gamma, IL-12 and IL-18 all are important in the development of Th1 cells. Th1 cells produce IL-2 and IFN-g, which in turn, promote the differentiation of fully cytotoxic T cells from CD8+ precursors.
A recent report published in Nature Medicine by Long et al. demonstrated a multi-fold higher expression of Th-1 cytokines, in particular, TNF alpha and IL-2, and significant expression of the IL-2 receptor subunit alpha in symptomatic COVID 19 patients in Wuhan.(16) A subsequent report published in Science Immunology by Lee et al. (17) demonstrated similar results through transcriptional and immuno-profiling techniques, and most recently a report in Nature (18) did the same. Therefore, among all immunomodulatory therapies, we view that targeting the Th1 response to be a key strategy. We propose targeting the IL-2R with Basiliximab.
Basiliximab (Simulect ®) is a monoclonal antibody against a subunit of IL-2 and is FDA approved for the treatment of acute renal transplant rejection, and is used off label in many other cases of transplant rejection mitigation.(2, 12) This agent has a long track record of safety and we believe among Th1 cytokine targets, to be a safe target for inhibition in SARS-COV2 induced cytokine storm.
Additional novel methodologies, including treatment with orally approved FDA approved JAK-STAT inhibitors (2) sirolimus (19-21) or calcineurin inhibitors (12) may serve as a broader opportunity to maintain suppression of inflammation following acute phase cytokine storm intervention with Basilixamab. One new area of interest is in complement mitigation, and inhibitors (eciluzimab) targeting this more teleologically more primal cascade may have a role (12, 22).
