Although graft-versus-host disease (GVHD) is a life-threatening complication of hematopoietic stem cell transplantation (HSCT), its current diagnosis mainly depends on clinical manifestations and invasive biopsies. Early diagnosis of GVHD, preferably based on unbiased laboratory screening tools, may increase the safety of allogeneic HSCT and thus further broaden its application to even larger patient populations. In the past, many efforts were made to use single-protein biomarkers, which were specific for infection or inflammation after allogeneic HSCT but not specific for acute GVHD. Although some of these reports seem to hold promise, in many cases there was a high probability that a single marker was not specific, thus making differential diagnosis of similar diseases difficult. It is reasonable to believe that the simultaneous monitoring of more than one protein or peptide within a sample holds greater promise for the differential diagnosis of diseases, including GVHD. Recently, the application of proteomic tools allowing screening for differentially expressed or excreted proteins in body fluids is becoming more important.
Using proteomics, a Japanese group from Saporo screened for plasma proteins specific for GVHD in a mouse model. One peak retained a discriminatory value in two diagnostic groups (GVHD and normal controls) with increased expression in the disease, decreased expression during cyclosporine treatment, and was barely detectable in syngeneic transplantation. Purification and mass analysis identified this molecule as CCL8, a member of a large chemokine family. In human samples, the serum concentration of CCL8 correlated closely with GVHD severity. All non-GVHD samples contained less than 48 pg of CCL8 per mL. In sharp contrast, CCL8 was highly up-regulated in GVHD sera. Strikingly, two patients with severe fatal GVHD had extremely high levels of CCL8. Thus, CCL8 seems to be a promising specific serum marker for the early and accurate diagnosis of GVHD.
In Brief
This study is of major importance for several reasons:
It confirms preliminary results reported by Weissinger and co-workers1 published in Blood in which authors describe the application of capillary electrophoresis coupled online with mass spectrometry to 13 samples from 10 patients with acute GVHD of grade II or more and 50 control samples from 23 patients without GVHD. About 170 GVHD-specific polypeptides were detected and as a result a tentatively acute GVHD-specific model consisting of 31 polypeptides was chosen, allowing correct classification of 13 of 13 acute GVHD samples and 49 of 50 control samples in a training set. The subsequent blinded evaluation of 599 samples enabled diagnosis of acute GVHD greater than grade II, even prior to clinical diagnosis, with a sensitivity of 83 percent and a specificity of 76 percent.
The study by Hori and colleagues took advantage of a murine model (in which many parameters could be controlled for) to set up the search for specific markers that allows the characterization of proteins following a huge amount of work that would not have been easily feasible from human samples analyzed by Weissinger and colleagues.1
CCL8 discovery makes the bridge even stronger between chemokines and acute GVHD pathophysiology. Indeed, the migration of cells from vascular to extra-vascular compartments implies a sequential cascade of events, involving interplay between adhesion molecules and chemokines. Acute GVHD requires that effector cells reach their target tissues. Lymphocytes do not enter specific tissues because they "recognize" a given antigen; they enter because they possess the requisite combination of homing receptors and chemokine receptors to engage the endothelium at the target tissue(s). Because GVHD is relatively organ-specific — principally affecting the skin, gut, and liver — our increasing knowledge of the pertinent adhesion molecules and chemokines directing effector-cell trafficking to these sites offers novel therapeutic approaches for prevention or treatment of GVHD.
Finally, the use of proteomics opens the door to exciting developments in the understanding of GVHD, the main one (at least in my opinion) being to use this tool to, finally, try to understand why and how some patients may develop a self-limited disease with an accompanying graft-versus-leukemia effect while others will develop a fatal steroid-resistant disease.
References
Competing Interests
Dr. Socié indicated no relevant conflicts of interest.
