Parent-progeny recognition as a function of MHC odortype identity.

The several linked polymorphic genes of the MHC, which has been proposed as a prime determinant of sensed genetic individuality within species, is known to operate in mice by olfactory recognition in aspects of reproductive behavior that concern mate selection, thereby favoring outbreeding and heterozygosity, and also concern the maintenance of pregnancy. A single base-change can alter an individual MHC odortype, and the potential range of combinatorial MHC-determined odortypes is clearly vast. Following our findings that newborn mice already express their MHC odortype (which is detectable at 9 days of gestational age), we sought to determine whether MHC is involved in behavioral aspects of early development, such as rearing. In the studies presented herein, we report the ability and proclivity of mothers to recognize and preferentially retrieve syngeneic (genetically identical) pups from other pups differing only for MHC. Reciprocally, we report the ability of pups to recognize their familial environment, regardless of whether they had been nursed by their biological mothers or by foster mothers. Early learning experiences of the MHC environment are apparently a key element in survival, assuring maternal protection and promoting outbreeding.

Effect of B2m gene disruption on MHC-determined odortypes.

Major histocompatibility complex (MHC) genes confer individual olfactory identity that can be detected with exquisite accuracy by mice. The fact that MHC genes themselves generate the characteristic odortype, rather than dedicated odor-determining genes, was supported in studies of point mutations in H2K and HLA transgenic mice, which evinced distinct odor profiles in olfactory assays. In this article we provide further evidence for a central role of MHC genes themselves in odortype specification by demonstrating that mice that are unable to express their genomic class I MHC genes because they lack beta2-microglobulin are distinguishable by scent from otherwise identical mice which possess an intact B2m gene. This odortype disparity appears at 9-12 days of gestational age, the period in which the MHC is first detectable in fetal cells of normal mice.

Odortypes: their origin and composition.

Odors that distinguish one individual from another member of the species and are determined by polymorphic genes are called odortypes. Odortypes and their considerable societal significance have been studied intimately only in mice and mainly with respect to the genes of the major histocompatibility complex. Further understanding and the matter of human relevance have been hampered by the apparent restriction of odortype expression to urine. The present finding that odorants comprising prerenal odortypes are already present in blood, albeit in masked form, affords the basis of a comprehensive view of odortypes. Accordingly, major histocompatibility complex and other polymorphic genes of antiquity are seen inter alia as agents of normal variation, which entails quantitative variation in output of odorant metabolites. Relatively few such normal variations should suffice for a vast range of compound odors whose specificity is determined by combinative assortment of the same set of individual volatile compounds.

Evidence suggesting that the odortypes of pregnant women are a compound of maternal and fetal odortypes.

Odortypes--namely, body odors that distinguish one individual from another on the basis of genetic polymorphism at the major histocompatibility complex and other loci--are a fundamental element in the social life and reproductive behavior of the mouse, including familial imprinting, mate choice, and control of early pregnancy. Odortypes are strongly represented in urine. During mouse pregnancy, an outcrossed mother's urine acquires fetal major histocompatibility complex odortypes of paternal origin, an observation that we took as the focus of a search for odortypes in humans, using a fully automated computer-programmed olfactometer in which trained rats are known to distinguish precisely the odortypes of another species. Five women provided urine samples before and after birth, which in each case appropriately trained rats were found to distinguish in the olfactometer. Whether this olfactory distinction of mothers' urine before and after birth reflects in part the odortype and hence genotype of the fetus, and not just the state of pregnancy per se, was tested in a second study in which each mother's postpartum urine was mixed either with urine from her own infant or with urine of a different, same-aged infant. Responses of trained rats were more positive with respect to the former (congruous) mixtures than to the latter (incongruous) mixtures, implying that, as in the mouse, human fetal odortypes of paternal genomic origin are represented in the odortype of the mother, doubtless by circulatory transfer of the pertinent odorants.

Immunoreactivity of umbilical cord blood and post-partum maternal peripheral blood with regard to HLA-haploidentical transplantation.

Recent clinical reports have demonstrated that umbilical cord blood (CB) may be utilized as a source of transplantable hematopoietic stem cells when bone marrow is not available. However, it is not apparent that CB can be used to transplant partially HLA-matched siblings or matched, non-familial recipients. In this study the immunoreactivity of CB has been investigated within familial confines; 14 families were analyzed at the time of birth of their child and six of these families were reassessed at 6 months post-partum. In mixed lymphocyte reactions, CB was unable to significantly respond to stimulation with cells from either the mother or father. Furthermore, unlike adult peripheral blood, CB displayed depressed immune responses to alloantigen and T cell mitogen. At 6 months, the immune responses of the infant demonstrated normal development in terms of alloantigen and mitogen responses. However, at 6 months both the mother and the infant demonstrated a continued immune tolerance to one another. The data suggest that CB could be used in familial transplant situations when siblings are HLA-haploidentical if the donor/recipients are chosen based on the paternal haplotype. Furthermore, maternal bone marrow harvested during the 6 months immediately following delivery of a child also should be suitable as a stem cell graft in haploidentical situations.

Discrimination of odortypes determined by the major histocompatibility complex among outbred mice.

Genetically determined body odors that distinguish one mouse from another are termed odortypes. The best known odortypes, highly expressed in urine, are those specified by H-2, the major histocompatibility complex of the mouse, but other odortypes originate from unidentified loci in the rest of the genome, including both sex chromosomes. The definition of H-2 odortypes and evidence that their perception affects reproductive behavior have so far depended on studies with inbred mouse strains whose genetic differences are confined to the H-2 complex of genes. To simulate feral conditions more closely, a freely segregating population was bred from crosses involving four unrelated inbred strains contributing four different H-2 haplotypes. After H-2 typing, this outbred population was divided into four groups of freely segregating mice, comprising the four distinct H-2 genotypes represented, to serve as conventional donors of urine for evaluation in the standard Y-maze system used in the training and testing of mice for H-2 odortype discrimination. With respect to utility in training mice for H-2 odortype discrimination, and to degrees of concordance attained in the Y-maze by trained mice, these urinary H-2 odortype sources from outbred mice were no less effective than urines customarily obtained for those purposes from nonsegregating inbred donors. We conclude that discrimination of H-2 odortypes is not appreciably affected or impaired by the usual concurrent segregation within the genome as a whole.

Collection, separation and cryopreservation of umbilical cord blood for use in transplantation.

Bone marrow transplantation (BMT) is limited by the paucity of HLA-matched donors and the frequent occurrence of graft-versus-host disease (GVHD). Recent clinical reports have implied that the use of umbilical cord blood (UCB) may alleviate some of the problems associated with BMT. Banks of frozen UCB could make the problem of finding suitable stem cell donors easier and stem cell grafts would be more readily available. However, definitive experiments are needed to develop optimal methods for collection, separation and storage of cryopreserved UCB for extended periods of time. We have found that several simple techniques may be utilized to collect large volumes of UCB (up to 220 ml). Also, modification of a common density gradient separation method permits recovery of large quantities of UCB mononuclear cells. Finally, we have examined the effects of prolonged frozen storage on the ability to recover viable and functional UCB, particularly stem/progenitor cells. It was observed that storage of UCB in liquid nitrogen for as long as 7 years had minimal effects on cell viability, cellular composition of UCB and progenitor/stem cell capacity. Thus, the establishment of UCB banks for use in transplantation appears to be a feasible approach.

Fetal H-2 odortypes are evident in the urine of pregnant female mice.

The major histocompatibility complex (MHC) imparts to each mouse an individual urinary odor, called "odortype", which reflects its MHC genotype. Perception of odortypes affects mate selection and embryonic implantation. Recent findings that odortypes are expressed as early as one day of age suggested that they might already be expressed in utero. We now report that at 9-12 days of gestation, odortypes specified by paternal (non-maternal) MHC haplotypes become apparent in maternal urine. Thus, odortypes are expressed in utero, can be sensed even before birth, and may serve in familial identification and communication.

Human bone marrow and umbilical cord blood cells generate CD4+ and CD8+ single-positive T cells in murine fetal thymus organ culture.

Murine fetal thymus lobes isolated from both normal and scid/scid mice can be colonized by donor cells from either human bone marrow or human umbilical cord blood in vitro. Subsequent organ culture results in a transient production of a few CD4+ CD8+ (double-positive) cells and then the accumulation of CD4+ or CD8+ (single-positive) T cells. A significant number of immature T-cell intermediates (e.g., CD8low, CD3-/low cells) were present in early organ cultures, suggesting that these were progenitors of the mature CD3+/high single-positive T cells that dominated late cultures. Depletion of mature T cells from the donor-cell populations did not affect their ability to colonize thymus lobes. However, colonization depended on the presence of CD7+ progenitor T cells. Limiting dilution experiments using mature T-cell populations (human peripheral blood leukocytes, human bone marrow cells, and human umbilical cord blood cells) suggested that thymic organ culture supports the growth of progenitor T cells but does not support the growth of mature human T cells. Each of these donor populations produced single-positive populations with different CD4/CD8 ratios, suggesting that precursor cells from different sources differ qualitatively in their capacity to differentiate into T cells.

Analysis of the hairless mouse as a model for the effects of aging on the immune system.

Studies into the effects of aging on the immune system are hampered by the lack of a suitable animal model that is readily available and cost efficient. The mutant mouse, hairless (hr/hr genotype), has been shown to undergo an accelerated thymic involution with accompanying immunodeficiency. Thus, this strain of mouse has been proposed as a model for studying the interactions of aging and immune function. We have investigated the effects of homozygous hr gene expression over time on the immune function of these mice. It was observed that homozygous hr gene expression had minimal effects on peripheral lymphocyte subset compositions but did appear to result in changes in thymic differentiation. Further, hr/hr mice displayed decreased proliferative responses to IL2 and mitogen stimulation, although cytotoxic responses (both NK and T cell mediated) appeared normal. These defects appear to be attributable to T helper cell dysfunction. Each of the changes found in hr/hr mice were distinct from those seen with age-matched control mice. Thus, the hr/hr inbred strain of mouse does not appear to be a suitable model for use in analyzing the effects of aging on the immune system.

Adoptive transfer of skin-selective autoimmunity induced by Skn alloantigenic disparities.

Two unlinked genes of the mouse, Skn-1 and Skn-2, each with alterative alleles, specify alternative cell-surface Skn alloantigens expressed only by epidermal and neural cells. C57BL/6 (B6) and A/J (A) strain mice differ at both Skn loci. Thus lethally irradiated B6 mice restored with (B6 x A)F1 hybrid hematopoietic cells [(B6 x A)/B6 chimeras] reject A strain (Skn-incompatible) skin grafts. Our studies were designed primarily to test the inference that (B6 x A)F1 lymphoid cells, after differentiating in B6 recipients, which lack the Skn alloantigens of A strain mice, may make an Skn-related, skin-selective autoimmune response when returned to their native (B6 x A)F1 habitat. Severe cutaneous lesions did, indeed, ensue after spleen cells of (B6 x A)/B6 chimeras were transferred to (B6 x A)F1 recipients, provided that three conditions were met--namely, (i) priming of the (B6 x A)/B6 chimeric donor by grafting and rejection of Skn-incompatible A strain skin grafts, (ii) stimulation of the recipient's skin as from shaving, at which sites the lesions were mainly located, and (iii) pretreatment of the (B6 x A)F1 recipients with cyclophosphamide or sublethal irradiation. Spleen cells of control female chimeras primed by grafting and rejection of H-Y (Skn-compatible) B6 male skin failed to incite the Skn-typical cutaneous lesions in (B6 x A)F1 recipients, indicating that these lesions were Skn-specific and not a nonspecific consequence of incompatible skin grafting per se. Normally compatible A strain skin grafts, but not Skn-compatible B6 skin grafts, were rejected by cyclophosphamide-treated (B6 x A)F1 recipients of (B6 x A)/B6 spleen cells from Skn-primed chimera donors. Treatment of primed chimeras' spleen cells with antiserum to H-2a (A strain) specifically abolished their capacity to adoptively incite the Skn-related autoimmune syndrome, confirming that the immune cells responsible are of (B6 x A)F1 origin and are not residual B6 derivatives. These findings add weight to the status of Skn systems as agents of tissue-selective histoincompatibility and, perhaps, of clinical disorders with a known or suspected autoimmune basis affecting the skin.

Phenotypic and functional immaturity of human umbilical cord blood T lymphocytes.

Successful implementation of bone marrow transplantation for hematopoietic reconstitution is limited by the lack of suitably HLA-matched donors and by the occurrence of graft-versus-host disease that frequently accompanies this procedure. Recent clinical reports have implied that the use of umbilical cord blood as a source of transplantable stem cells may solve these problems. To date, definitive experiments have not been performed to assess the immunological potential of T cells found in umbilical cord blood, which could mediate graft-versus-host disease. In the present study we have observed that umbilical cord blood contains T lymphocytes that appear to be phenotypically immature. In addition, umbilical cord blood lymphocytes appeared to be functionally immature as shown by minimal responses to stimulation with interleukin 2, phytohemagglutinin, or alloantigens. Thus, umbilical cord blood may be more suitable for allogeneic transplantation than bone marrow in that these cord blood cells may not be as capable of mediating graft-versus-host disease.

Expression of urinary H-2 odortypes by infant mice.

The extended H-2 complex of genes in the mouse includes at least three loci that independently specify distinctive body odors, "odortypes," whose differential recognition influences mating choice and affects the maintenance of early pregnancy. A prime experimental method of identifying H-2 odortypes is the specially designed Y-maze in which mice are trained, by water deprivation and reward, to distinguish odors conducted to the arms of the maze from H-2-dissimilar mice or their urines. It is confirmed that H-2-dissimilar infant mice, unlike adult mice, are not distinguished by trained mice in the Y-maze. However, a previous conclusion that infant mice do not express H-2 odortypes is shown to be incorrect, because the urines of H-2-dissimilar infant mice, even at 1 day of age, were distinguished in the Y-maze. Thus urine, ingested by the mother, clearly could suffice for her to distinguish her own from other H-2-dissimilar pups. Further, urine would seem to be a unique source of H-2 odortypes. If, as we believe, H-2 odortypes represent mostly compound odors composed by H-2 genetic variation in the urinary output of odorous metabolites, as distinct from simple odors that depend on chemical differences of single odorants, then the kidney, which is not responsible for H-2 odortype specificity, may nevertheless impart a unique character to urinary odortypes by virtue of differential excretion/resorption processing of various constituent odorous metabolites. In that case, various organs and tissues, among which the hematopoietic/lymphoid system is known to contribute to H-2 odortype specificity, may exhibit tissue-specific varieties of H-2 odortypes, their products having not yet been subjected to renal processing.

Expression of type IV collagenase correlates with the invasion of human lymphoblastoid cell lines and pathogenesis in SCID mice.

An in vitro model, called the Membrane Invasion Culture System (MICS), was used to study the invasive potential of an Epstein-Barr virus (EBV) positive lymphoblastoid cell line (LCL), an EBV-negative Burkitt lymphoma (BL) cell line of American origin and an EBV-positive BL of African origin. MICS measured the ability of these cell lines to invade reconstituted basement membrane-coated filters, which correlated with their tumorigenic and metastatic capabilities in a SCID mouse model. Furthermore, the significantly greater invasive behaviour of the EBV-positive LCL was directly correlated with the cells' ability to express and secrete human type IV collagenase (72 kDa), an important metalloproteinase responsible for the degradation of collagen IV in basement membranes. The data suggest that MICS and the SCID mouse are useful tests of tumorigenicity in lymphoid cells, with measurable effects in both systems related to human type IV collagenase activity. Both models allow further exploration of malignant phenotypes associated with EBV transformation of lymphoid tissues.

Umbilical cord blood hematopoietic stem and repopulating cells in human clinical transplantation.

This paper reviews our recent laboratory and clinical studies demonstrating the efficacious use of human umbilical cord blood for HLA-matched allogeneic sibling stem/progenitor cell transplantation in cases of Fanconi's anemia. Future implications and potential problems are discussed with regards to (a) the possibility of maternal cell contamination, (b) the broadness of applicability with regards to other diseases that might be transplanted, and whether such transplants are feasible in adults, as well as in children, and (c) the immunological reactivity of cord blood cells, and whether these cells can be used to cross histocompatibility barriers more easily than that of bone marrow from adults.

Odor types determined by the major histocompatibility complex in germfree mice.

The major histocompatibility complex (MHC) is the prime but not exclusive determinant of genetically specific constitutive body odors, termed odor types, represented strongly in urine of the mouse. Perception of MHC-determined odor types influences reproductive behavior in the contexts of mate choice and maintenance of early pregnancy, tending to favor the propagation of one MHC type over another. How MHC genotype determines MHC odor type is unknown. One possible explanation is that differential odorants are generated by populations of commensal microorganisms whose composition is somehow geared to MHC diversity. This hypothesis was tested in the Y-maze system in which mice are trained to distinguish the urinary odors of MHC-congenic mice. First, it was shown that mice could readily be trained to distinguish the urines of germfree MHC-congenic mice. Second, it was shown that mice trained to distinguish the urines of conventionally maintained MHC-congenic mice could as readily distinguish the urines of germfree MHC-congenic mice. These results imply that MHC-determined odor types do not depend on odorants generated by microorganisms.

Regulation of alternative splicing in the generation of isoforms of the mouse Ly-5 (CD45) glycoprotein.

Alternative splicing generates various Ly-5 glycoprotein isoforms of the cell surface that typify different cell lineages and stages of hematopoietic differentiation in the mouse; exons 4-6 are incorporated to generate a B-cell isoform (B220) and excluded from a T-cell isoform (T200), the other coding exons (3 and 7-33) being shared. As a first step to understanding the mechanisms regulating Ly-5 alternative splicing, and thus determining Ly-5 isoforms, a minigene representing exons 3-7 was transfected into Ly-5-expressor T cells and B cells and into nonexpressor L cells for comparison of splicing patterns. We conclude that all the information required for faithful splice-site selection according to cell type is contained within the resulting pre-mRNA. The splicing pattern manifested by nonexpressor L cells may represent a default and nonregulated type. We postulate trans-acting factor(s) to account for the selection of appropriate exons, and we provide support for this interpretation from analysis of fused hybrid T-B cells, which exhibited B-cell specific Ly-5 transcripts. Splicing patterns were well conserved despite substantial disruption of constructs. However, extensive deletion analyses suggested that cis sequences flanking and within exon 6 affect the exclusion of that exon in T cells.

Chemosensory identity and the Y chromosome.

Genes in the extended major histocompatibility complex (MHC) of the mouse (H-2: Qa:T1a) impart to each mouse an odor that reflects its genetic constitution at this region of chromosome 17. Sensory recognition of these differential odors influences reproductive behavior and evokes neuroendocrine responses critical to the maintenance of pregnancy. To determine whether other parts of the mouse genome contribute to individual odor, and so may similarly exert a selective force on loci other than the MHC, mice differing genetically only in their X and/or Y chromosomes were tested for individuality of scent in the Y-maze system previously employed to investigate MHC-related scent distinctions. It was found that the X and Y chromosomes each confer individuality of scent related to genotype, but differences at the H-2 locus are considerably more salient. Nevertheless, chemosensory cues controlled by differences on the Y chromosome could play a role in individual recognition, mate selection, aggressive interactions, and perhaps other aspects of mouse chemosensory behavior.