Biomedical Engineering Reference
In-Depth Information
Classi fi cation of SC Transplants
The use of high-dose radio-chemotherapy (conditioning regimen) followed by the
transplant of allogeneic or autologous SCs is considered an effective treatment for
hematological malignancies. In the last few years, the use of such a procedure was
proposed also for non-hematopoietic neoplastic disorders (neuroblastoma, breast
carcinoma, Wilms tumor, melanoma, lungs carcinoma) and also for some autoim-
mune disorders (sclerosis multiplex).
Autologous transplants
. When is BM appropriate to use as a source of SCs for
autologous resuscitation following myeloablative radio-chemotherapy or RIC
depends on the marrow general state and/or infiltration with malignant cells. Fibrosis
makes marrow not possible for SC collection by aspirations. Tumor cell infiltrates
eliminate marrow as a transplant source as well. Prior pelvic irradiation, poor anes-
thesia risk, obesity, or patient refusal of marrow collection can limit marrow as an
option. Mobilized autologous SCs from PB are commonly used in the above situa-
tions and in heavily treated patients. This procedure is nowadays in routine clinical
practice and provides more progenitor cell yield than conventional marrow harvest
and therefore earlier engraftment, that is, a faster hematopoietic recovery. Primarily
for this reason, transplant of PB-derived SCs has practically replaced BM transplant
in an autologous setting. As mentioned, autologous PB harvests involve mobilizing
the SCs from the patient's BM compartment into the circulation using different
growth factors, typically in combination with chemotherapy prior to collection.
Once in the circulation, the SCs are collected by apheresis—conventional or large-
volume leukapheresis [
6,
38
] .
Allogeneic transplants
. Transplant of allogeneic SCs is indicated in the treatment of
patients with malignant disease—if they have HLA-matched donors. For patients
with immunodeficiency, marrow failure, metabolism disorders, etc., the use of allo-
geneic SCs is imperative. However, there are also some atypical data related to
treatment of severe aplastic anemia using autologous SCs [
40
] . Allogeneic trans-
plant is associated with a risk that immunocompetent donor cells will react again
recipient tissues (GvHD), despite immunosuppressive therapy administered. In
adult “related allogeneic setting,” the best results are obtained using completely
HLA-matched (HLA-identical, i.e., six-antigen-matched donor/recipient pairs)
transplants. There is a 25% chance of a sibling being a complete match, a 50%
chance of a haplotype match, and a 25% chance of a complete mismatch. Pediatric
patients are more tolerant of partially mismatched graft [
1-
4,
36
] .
Data obtained up till now has shown that the use of SC donor registers can
successfully recruit unrelated donors for collection of BM- or PB-derived SCs.
Thus, matched unrelated donor (MUD) searches can be initiated for approxi-
mately 70% of candidates without sibling donor. These protocols are superior
because of high SC-grafting potential (allogeneic vs. autologous cells), following
rapid hematopoietic reconstitution, and of GvL effect [
36,
47
] . For de fi nitive
choice, additional experimental and clinical trials for comparison of efficacy and
