Developments in non-flow cytometry

A novel, inexpensive, and easily performed non-flow cytometric method called CD4 Select was presented by Thai researchers in 2008. It counts CD4 cells using an automatic haematology analyser (equipment used for performing complete blood counts). The results for absolute CD4 counts and CD4 lymphocyte percentage correlated closely with results from standard flow cytometry. The CD4 Select can be used in small or rural settings and offers relatively high sample throughput, while being less labour intensive than other non-flow cytometric methods.

The test reagent, CD4 Select, is generated by binding the MT4 monoclonal antibody (mAb) to ferrous beads. MT4 binds strongly to the CD4 molecule on CD4 lymphocytes (CD4 T-cells), but weakly or not at all to the CD4 on monocytes, so MT4 can be used to tag CD4 T-cells in blood samples with a high degree of specificity. When the CD4 Select reagent is combined with the blood sample, CD4 cells become bound to the beads and are then magnetically removed from the sample. The percentage of CD4 lymphocytes can be calculated by subtracting the lymphocyte count in this CD4-depleted sample from the total lymphocyte count in a second, unaltered sample from the same patient; the absolute CD4 lymphocyte count is then derived from the percentage. Turnaround time is less than one hour.¹

A Ugandan study found that although the use of dynabeads and hydrospheres each underestimated CD4 lymphocyte count compared with flow cytometry, in resource-limited areas with small daily volume, manual bead-based assays might be an alternative to flow cytometry.²