Novel 2 Marker Sandwich Immunoassay for the Detection of Precursor- and Mature Granulocyte-Derived Exosomes in Peripheral Blood: A Preliminary Case Study

Introduction:

In order to assess hematopoietic precursor cells, bone marrow biopsies are routinely conducted, which is painful for the patient and is not applicable for frequent testing. However, precursor, maturating, and matured cells are known to produce exosomes, which are released into peripheral blood. By analyzing these exosomes in plasma, bone marrow condition may be assessed noninvasively.

Myeloid precursor cells express different surface markers than when they have matured. It is reasonable to speculate that these markers would be incorporated into exosomes. In this study, we developed a novel sandwich enzyme-linked immunosorbent assay (ELISA) by using a combination of monoclonal antibodies against 2 different leukocyte antigens, to account for the number of exosomes in plasma.

Methods

In 6 patients undergoing chemotherapy, venous blood was drawn at regular intervals before, during, and after respective chemotherapies was given. Various clones of monoclonal antibodies against CD11b, CD33, CD34, CD35, CD81, and CD117 were obtained, and antibodies were biotinylated by EZ link Sulfo-NHS-LC-Biotin. Anti-brain antibodies were switched with anti-leukocyte antibodies, and exosome activity was trended.

Results

CD11b+ and CD 117+ plates showed small changes during chemotherapy (within +/- 50% of the initial value), while plasma WBC count showed a dramatic decrease during chemotherapy.

In the recovery phase of WBC after chemotherapy, CD11b+ and CD16+showed a greater than 2-fold increase, with the up-trend taking place earlier than its plasma WBC counterparts. CD 117+ CD33+ also showed an up-trend, but was slower than their CD11b+ and CD16+ counterpart.

Finally, each exosome value was divided by other markers to calculate the ratio, and compared between pre and post chemotherapy blood. In half of the cases, there was not a difference, versus an almost double premature/mature ratio in post-chemotherapy blood in the other half of patients.

Conclusion

From data collected from pre-chemotherapy studies, the lack of correlation between ELISA data compared to plasma WBC data, indicates that plasma exosome analysis might not be suitable for the monitoring of acute bone marrow suppression.

Additionally, in the recovery phase, surface markers correlation with WBC was present in only some of the markers, indicating that the assay sensitivity is dependent on the marker combinations.

Overall, both myeloid precursor- and mature granulocyte-derived exosomes were increased during the recovery from chemotherapy in 3 out of 5 patients, and exosome profiles were different after chemotherapy in 2 out of 5 patients.