CD4 and COVID-19: Subsequent studies elucidated a more complex immunophenotype for COVID-19, with profound changes in both myeloid and lymphoid leukocyte populations, including mobilization of immature myeloid cells from the bone-marrow [13–15], an increase in circulating B-cell plasmablasts and an overall lymphopenia including CD4, CD8, and invariant (γδ) T cells.