Method of diagnosis and kit therefor

A method for evaluating in a blood sample from a subject the number of T-cells bearing CD4, the method comprising:

• (i) contacting the sample with an agent capable of lysing or permeabilizing CD4 T-cells prior to step (ii);
• (ii) contacting the sample with an antibody or antigen-binding fragment thereof that specifically binds to the cytoplasmic domain of CD4 and forms a CD4-antibody complex;
• and
• (iii) directly or indirectly detecting and evaluating the level or presence of CD4-antibody complex formed in step (ii);
• and
• wherein the level or presence of the CD4-antibody complex formed in step (ii) comprising the CD4 cytoplasmic domain is indicative of the number of CD4 bearing T-cells in the subject, and wherein the antibody or antigen-binding fragment thereof in step (ii) does not detect soluble CD4 lacking the cytoplasmic domain and thereby, distinguishes between cell-associated CD4 comprising the cytoplasmic domain and soluble CD4 lacking a cytoplasmic domain.