Transplantation
Stem cell transplantation (HSCT) 1: clinical indications and types of HSCT
Clinical indications
Combined immunodeficiency where there is reason to suspect progression, including:
Wiskott-Aldrich syndrome
hyper-IgM syndrome
activation defects (ZAP70 kinase deficiency, etc.)
MHC antigen deficiency (class I, class II)
X-linked lymphoproliferative disease
purine nucleoside phosphorylase deficiency
cartilage-hair hypoplasia
DiGeorge syndrome (severe thymic transplants also used)
chronic mucocutaneous candidiasis
CD40 ligand deficiency.
Neutrophil disorders:
chronic granulomatous disease
leucocyte adhesion molecule deficiency (LFA-1 deficiency)
Chediak-Higashi syndrome (in accelerated phase)
Griscelli syndrome
Schwachmann-Diamond syndrome.
Inherited metabolic diseases:
osteopetrosis
Gaucher’s disease
adrenoleucodystrophy
metachromatic leucodystrophy
mucopolysaccharidoses (Hurler’s syndrome, Maroteaux-Lamy syndrome, Hunter syndrome)
Lesch-Nyan syndrome.
Marrow failure:
Fanconi anaemia
aplastic anaemia
thalassaemia major
congenital anaemia (Diamond-Blackfan syndrome).
Lymphoma, leukaemias, myeloma, usually when in remission.
Solid tumours (Ewing sarcoma, neuroblastoma, germ cell tumours, breast and ovarian cancer).
Juvenile chronic arthritis.
Types of HSCT
HSCT involves the reconstitution of the full haematopoietic system by transfer of pluripotent stem cells. This may be as unpurified bone marrow or manipulated to enrich stem cells.
It can be classified according to donor source and site of harvest of stem cells.
Allogeneic—another genotypically matched individual acts as donor of stem cells. May be a sibling or matched unrelated donor (MUD).
Autologous—patient acts as own source for stem cells.
Bone marrow stem cells procured from direct puncture and aspiration of bone marrow before intravenous re-infusion.
Peripheral stem cells—stem cells liberated into peripheral circulation and then collected by apheresis.
Cord blood stem cells—stem cells collected from umbilical cord blood after delivery. These may come from cord blood stem cell banks.
All sources of bone marrow/stem cells may undergo in vitro manipulation to remove mature T cells (T-cell depletion) or accomplish stem cell (CD34+) enrichment.
T-cell depletion can be achieved by:
soya bean lectin and sheep erythrocyte agglutination
Campath® antibody plus complement
sheep erythrocyte agglutination.
T-cell depletion and CD34+ stem cell enrichment may also be achieved by magnetic bead separation.
Type of manipulation may depend on underlying condition.
Stem cells sourced from peripheral blood have 10-fold more mature T cells than stem cells isolated from bone marrow.
HSCT 2: conditioning and matching
Conditioning
Conditioning is required to eliminate residual immune system and allow incoming stem cells to engraft.
Recipient is treated with cytoreductive therapy including busulfan and cyclophosphamide.
This leads to a severe aplastic phase during which isolation to laminar flow isolation and supportive transfusion are required.
Complications of this phase include:
veno-occlusive disease
alopecia
severe mucositis
immune suppression predisposing to wide variety of potentially fatal infections.
Prophylactic IVIg, antibiotics, antifungals, and antivirals are used routinely.
Regular surveillance and prompt treatment of infection is mandatory.
Long-term complications include:
infertility
hypothyroidism
secondary malignancy
late sepsis due to hyposplenism
psychological disturbance.
Reduced intensity or non-myeloablative conditioning regimes may be used in patients unable to tolerate the more toxic myeloablative chemotherapy.
For many patients with SCID, donor stem cells may engraft without conditioning due to lack of recipient T-cell numbers and function normally required to reject a stem cell graft.
Matching
MHC matching is required for all allogeneic transplants.
Success of the transplant is dependent on the match. Preferred sources are ranked in the following order:
(1) identical sibling matches
(2) matched unrelated donors
(3) if neither are available, haplo-identical parental bone marrow or bone marrow from less well-matched unrelated donors can be used.
Where a SCID baby requires a haplo-identical marrow, paternal marrow is preferred to eliminate any residual maternofetal engraftment.
Fully matched whole marrow can be used from an identical.
Where there are mismatches, in vitro or in vivo T-cell depletion is used to remove mature T cells that are capable of producing GvHD.
Matching procedures (see Chapter 21)
Confirmation of the suitability of the chosen donor is checked pre-transplant by molecular typing.
Mixed lymphocyte reactions (MLR) and CTLp or HTLp frequency (Chapter 21) have been used in the past but are not commonly used now.
High levels of reactivity in these tests are good predictors of the development of GvHD.
Immunosuppressants, including ciclosporin, methotrexate, mycophenolate mofetil, and steroids, are administered to reduce the risks of development of GvHD.
Marrow donation
Donors are assessed medically and screened for transmissible infections, including EBV, HIV, CMV, and parvovirus.
If there is a mismatch of viral status between donor and recipient, prophylactic antivirals may be used.
Whole marrow donors have to undergo a general anaesthetic for harvest, so cardiorespiratory fitness is essential.
Marrow is now tested routinely for stem cell numbers to assess the quality of the graft.
Stem cell harvesting
Peripheral stem cell harvesting is also being used for patients with marrow that would be unsuitable for harvesting (i.e. infiltrated with tumour).
In the autologous setting the advantages are:
better stem cell yield;
less contamination with tumour cells.
In the allogeneic setting the advantages are:
easier to collect from the donor’s perspective;
faster engraftment.
This can be augmented by administration of colony-stimulating factors (CSFs) to donor prior to apheresis.
Donors of the bone marrow may also be used as apheresis donors for neutrophils to provide cover due to the aplastic phase post-transplant.
Procedural considerations
Use of growth factors (G-CSF, GM-CSF) post-BMT in the recipient may speed up the reconstitution process and shorten the aplastic phase in the recipient.
There are concerns about long-term leukaemic risk from use of CSFs.
All recipients must receive irradiated cellular blood products to prevent accidental engraftment of viable donor lymphocytes until there is evidence of satisfactory immunological recovery.
HSCT 3: post-transplant monitoring
Post-transplant immunological monitoring has an important role in optimizing management and, in particular, for assessing the return of adaptive immunity. Frequency of monitoring depends on clinical status. Monitoring should include the following.
Full blood count
Indicates need for red cell and platelet support.
Rise of the neutrophil count gives a good indication of when adequate protective innate immunity has returned.
Neutropenia post-BMT may last between 9 and 21 days.
Neutropenia beyond 21 days suggests that stem cells have failed to engraft.
Lymphocyte subsets
Demonstrate when safe levels of CD4+ T and B cells have returned.
Very rapid rises in B cells in the absence of T cells usually indicate B-lymphoproliferative disease secondary to EBV.
These should be done at least monthly, or more often if there are problems.
A basic panel will include CD4, CD8, CD3, CD16/56, CD25, HLA-DR, CD19, or CD20.
Other markers in combination (CD45RA, CD45RO, CD27) may be helpful in monitoring immune reconstitution in greater depth.
Acute-phase proteins (CRP)
Provide early warning of infection.
Regular monitoring is required.
Immunoglobulins
Lymphocyte proliferation assays
Chimerism studies
Genetic techniques (RFLP, FISH, karyotype) now allow analysis of the origin of separated cell lineages (using monoclonal antibody coupled to magnetic beads).
In suitable patient-donor pairs, use of fluorescent anti-MHC antibodies may provide rapid information on the origin of cells (host or donor).
B-cell recovery is often host even when T cells are donor.
Despite this, there is usually full immunological recovery of B-cell function even if there is an MHC mismatch between T and B cells.
Other functional tests
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