Anti-C1 domain antibodies that accelerate factor VIII clearance contribute to antibody pathogenicity in a murine hemophilia A model.

Essentials Inhibitor formation remains a challenging complication of hemophilia A care. The Bethesda assay is the primary method used for determining bleeding risk and management. Antibodies that block factor VIII binding to von Willebrand factor can increase FVIII clearance. Antibodies that increase clearance contribute to antibody pathogenicity. SUMMARY: Background The development of neutralizing anti-factor VIII (FVIII) antibodies remains a challenging complication of modern hemophilia A care. In vitro assays are the primary method used for quantifying inhibitor titers, predicting bleeding risk, and determining bleeding management. However, other mechanisms of inhibition are not accounted for in these assays, which may result in discrepancies between the inhibitor titer and clinical bleeding symptoms. Objectives To evaluate FVIII clearance in vivo as a potential mechanism for antibody pathogenicity and to determine whether increased FVIII dosing regimens correct the associated bleeding phenotype. Methods FVIII-/- or FVIII-/- /von Willebrand factor (VWF)-/- mice were infused with anti-FVIII mAbs directed against the FVIII C1, C2 or A2 domains, followed by infusion of FVIII. Blood loss via the tail snip bleeding model, FVIII activity and FVIII antigen levels were subsequently measured. Results Pathogenic anti-C1 mAbs that compete with VWF for FVIII binding increased the clearance of FVIII-mAb complexes in FVIII-/- mice but not in FVIII-/- /VWF-/- mice. Additionally, pathogenic anti-C2 mAbs that inhibit FVIII binding to VWF increased FVIII clearance in FVIII-/- mice. Anti-C1, anti-C2 and anti-A2 mAbs that do not inhibit VWF binding did not accelerate FVIII clearance. Infusion of increased doses of FVIII in the presence of anti-C1 mAbs partially corrected blood loss in FVIII-/- mice. Conclusions A subset of antibodies that inhibit VWF binding to FVIII increase the clearance of FVIII-mAb complexes, which contributes to antibody pathogenicity. This may explain differences in the bleeding phenotype observed despite factor replacement in some patients with hemophilia A and low-titer inhibitors.

Characterization of a genetically engineered mouse model of hemophilia A with complete deletion of the F8 gene.

UNLABELLED: ESSENTIALS: Anti-factor VIII (FVIII) inhibitory antibody formation is a severe complication in hemophilia A therapy. We genetically engineered and characterized a mouse model with complete deletion of the F8 coding region. F8(TKO) mice exhibit severe hemophilia, express no detectable F8 mRNA, and produce FVIII inhibitors. The defined background and lack of FVIII in F8(TKO) mice will aid in studying FVIII inhibitor formation. BACKGROUND: The most important complication in hemophilia A treatment is the development of inhibitory anti-Factor VIII (FVIII) antibodies in patients after FVIII therapy. Patients with severe hemophilia who express no endogenous FVIII (i.e. cross-reacting material, CRM) have the greatest incidence of inhibitor formation. However, current mouse models of severe hemophilia A produce low levels of truncated FVIII. The lack of a corresponding mouse model hampers the study of inhibitor formation in the complete absence of FVIII protein. OBJECTIVES: We aimed to generate and characterize a novel mouse model of severe hemophilia A (designated the F8(TKO) strain) lacking the complete coding sequence of F8 and any FVIII CRM. METHODS: Mice were created on a C57BL/6 background using Cre-Lox recombination and characterized using in vivo bleeding assays, measurement of FVIII activity by coagulation and chromogenic assays, and anti-FVIII antibody production using ELISA. RESULTS: All F8 exonic coding regions were deleted from the genome and no F8 mRNA was detected in F8(TKO) mice. The bleeding phenotype of F8(TKO) mice was comparable to E16 mice by measurements of factor activity and tail snip assay. Similar levels of anti-FVIII antibody titers after recombinant FVIII injections were observed between F8(TKO) and E16 mice. CONCLUSIONS: We describe a new C57BL/6 mouse model for severe hemophilia A patients lacking CRM. These mice can be directly bred to the many C57BL/6 strains of genetically engineered mice, which is valuable for studying the impact of a wide variety of genes on FVIII inhibitor formation on a defined genetic background.

Delayed childbearing in the U.S.: facts and fictions.

PIP: Between 1970-82, the proportion of 1st births in the US to women 25 and older rose from 19-36% and the proportion of women still childless at ages 25-34 increased by 56% at about the same time. Although a sharp contrast with the baby boom era of the 1950s and 1960s, todays's epidemic of delayed childbearing is similar to patterns earlier in the 20th century. As then, much is due to delayed age at marriage, but baby boomers now in the their late 20s and early 30s are also delaying childbirth after marriage. The trend stems in part from their economic difficulties as they compete in a tight job market caused both by their large numbers and a turbulent economy. But it is also related to women's increasing education and, in turn, increasing opportunities in and commitment to the labor force, which can be expected to encourage a delayed childbearing even after prospects brighten for young people. Although a diverse group, most of today's delayed childbearers are white, highly educated, 2-career couples. Adequate daytime care for preschool children is a prime concern. Although more employers now offer childcare assistance and flexible work schedules to working parents, the juggle between jobs and childraising can be a strain. On the plus side are delayed childbearers' greater maturity and generally higher incomes, which can ease potential problems created by parent-child age differences as their children grow up. Businesses have been quick to respond to the new market of older, affluent, 1st-time mothers. New methods of treating of circumventing infertility and prenatal detection of chromosomal birth defects can now help overcome potential biological problems that may concern women who choose to delay childbearing past age 30.^ieng

Adolescent pregnancy and childbearing - growing concerns for Americans.

PIP: The negative impact of the increase in sexual activity among teen-agers and the health and life chances of those involved are examined. The barriers to effective contraception by teen-agers, racial differences, and the U.S. experience in relation to that of other countries are discussed. Some of the major topics discussed are: 1) overall fertility rates among teen-agers, 2) legitimate and illegitimate births, 3) marriage among teen-agers, 4) adoption, 5) abortion as an outlet, 6) sexual activity, 7) patterns in conceptions, and 8) patterns of contraceptive practice. Also discussed are: 1) teen-agers and clinical services, 2) health consequences of adolescent childbearing, 3) teen-agers health and sex, 4) child development, 5) life chances for a t een-age mother, 6) consequences for society, and 7) international comparisons. 6 figures and 11 tables are included.^ieng

Modernism and contraceptive use in Colombia.

This analysis addresses the question of whether fertility can be lowered without the prior occurrence of the social and economic changes that have come to be labeled modernization. The data show that there exists in Colombia a relatively high level of motivation to control fertility that, for many women, is not coupled with both knowledge of and access to a method of contraception. For the "traditional" woman, the problem may not be lack of motivation so much as lack of access to methods that she is aware of, such as the pill, and lack of knowledge of methods that require few resources of supplies, such as rhythm and withdrawal.

PIP: An analysis of the attitudes of Colombian women towards contraceptive use and actual contraceptive behavior indicates that knowledge of contraceptive techniques and access to supplies is critical to contraceptive use. Whether fertility can be significantly lowered without the prior occurrence of modernization has been questioned. In order to discover if there is motivation for family planning in Colombia, a developing country, independent of modernization, the results are examined of the National Fertility Study conducted in 1969 by the Colombian Association of Medical Faculties as a collaborative project with the Program of Comparative Fertility Studies in Colombia. 2951 married women or women living in consensual union in urban and rural areas were interviewed. Findings indicate that modern women, those of higher socioeconomic status, higher levels of schooling and of urban residence, are more likely to use fertility control methods and have fewer children. However, further analysis indicates that a favorable attitude toward family planning is independent of contraceptive use and that knowledge of contraception is strongly related to modernism and contraceptive use. Because urban women are generally more knowledgeable than rural women about all methods of contraception and the percent of all women claiming knowledge of each method increased with schooling level, lack of contraceptive knowledge rather than modernism is proposed as a critical factor in failure to practice birth control. In addition, traditional women are shown to be as likely as modern women to use contraceptive methods which did not require supplies and less likely to use those requiring technical knowledge. Consequently, cost and accessibility appear to be critical factors in contraceptive use. This demonstration that inadequate knowledge of birth control methods or restricted access to contraceptive supplies was probably more responsible for the limited practice of birth control in Colombia than were motivational factors associated with modernism would appear to keep open the possibility that widespread contraceptive practice can be achieved without modernizing the entire society.