HLA Resources

Histoimmunogenetics Markup Language (HML)


The National Marrow Donor Program® (NMDP) is a Registry of over seven million potential volunteer donors. We are committed to eliminating barriers to unrelated stem cell transplantation (USCT). One of the outstanding issues in the USCT process is the extended time necessary to identify an appropriately matched donor. Currently, the low/intermediate resolution HLA typing results in the NMDP Registry are condensed to allele codes, which can decrease the specificity of the typing and result in increased numbers of donors appearing as potential matches. In many cases, this translates into longer search times and additional costs for further HLA testing to find a suitable donor. The collection and utilization of primary HLA typing data could alleviate this issue through analysis of the true patterns of polymorphism underlying the coded results (Rev Immunogenet 2000;2(4):449-60 1). It is the desire of the NMDP, in collaboration with the USCT community, to reduce search times by optimizing primary data and result collection formats from all HLA typing laboratories.

In order to facilitate the electronic reporting of HLA testing results and the collection of the raw probe, primer and sequence data, the NMDP Bioinformatics group developed a software reporting format in 1998 but maintenance and extension became increasingly difficult due to the rigid format limitations. Therefore, the NMDP Bioinformatics group developed an XML-based reporting format to address the shortcomings of the previous format. The XML-based format is called Histoimmunogenetics Markup Language (HML) and is intended as a potentially general-purpose format for exchanging genetic typing data.

HML supports:

  • HML version 0.3.3 supports reporting of paired genotype allele lists as determined from Primary DNA Results (SSO, SSP and SBT)
  • Reporting genetic typing results using WHO nomenclature, and/or
  • Describing the results of any/all tests performed to generate genetic typing results (raw data). These tests include:
    • Sequence Specific Oligonucleotide Probing
    • Sequence Specific Primer Amplification
    • Sequence Based Typing
    • Reference Strand Conformational Analysis

The data dictionary document provides a single convenient and comprehensive reference.


HML Versions

Details about each HML version are available at the links listed below. Please send all questions and comments to

NEW - HML Version 0.3.3

Version 0.3.3 Examples and DTD. 

HML Version 0.3

Version 0.3 Examples and DTD. 

HML Version 0.2

Version 0.2 Examples and DTD.  

HML Version 0.1

Document Type Definition 0.1 (DTD) 


Information about DTDs and XML in general may be found on the W3C Web site at



  1. Rev Immunogenet 2000;2(4):449-60