Although the women were given top-of-the-line electric breast pumps and lots of instruction and encouragement, Morton soon noticed that the first few subjects enrolled in the study were expressing only a fraction of their colostrum (the body's precursor to milk).
CD133 is not expressed in all tumors, and expressed only a small fraction of the tumor cells in CD133-positive tumors.
Although several genes have been identified that significantly impact breast cancer risk when mutated or aberrantly expressed, only a small fraction of the overall population risk can be attributed to these genes [ 10- 12].
Another genetic marker of chordomas is chondroitin sulfate proteoglycan 4 (CSPG4), which has also been targeted for immunotherapy; however, this antigen is expressed only by a fraction (~62%) of these tumors [ 53] and could therefore produce false negative diagnoses.
Therefore significant expressional changes in genes expressed only in a small fraction of cells may be diluted by the expressional "noise" by cells of the surrounding tissue.
He found that one protein, called CD271, was always expressed on only a fraction of the cells in the human melanoma samples tested: The proportion of cells expressing CD271 varied in the samples from 2.5 to 41percentt of the total cell population; the marker appeared on a mean of 16.7percentt of cells in the samples.
For those proteins with either low or transient surface expression it seems likely that either the level of antigen on the surface is insufficient to promote bactericidal killing or, for transiently expressed proteins, only a fraction of the population may be killed.
In the outlier's scenario, a cancer gene is differently expressed in only a fraction of tumors.
However, the known CT antigens are expressed in only a fraction of cases of a given tumour type, and the progressive loss of tumour antigens is due to the immunoselection in the course of vaccination, the identification of additional CT antigens is urgently needed for developing polyvalent tumour vaccines to improve the efficacy of immunotherapy (Kalos, 2003).
To exclude a potential contribution for elicited anti-PMIF in the clearance of free parasites after schizont release, we also confirmed that PMIF is expressed only in the cytosolic fraction and not on membranes (Supplementary Figure 4i).
