The adaptive immune system, comprising humoral (or B cell mediated) and cytotoxic (or T cell-mediated) responses, has evolved to attack specific molecular features on their respective targets. The occurrence of one response to a specific target provides a host with “memory” of it, giving it a capability to mount a stronger response if the same target were to appear another time. Usually any protein or polysaccharide can serve as the target for some subset of the adaptive immune response cells or their products that recognize specific molecular features, or epitopes, on the target.
Since autoimmune disease involves the recognition by some component of the adaptive immune system to self targets, aspects of the adaptive immune system have been examined to aid in diagnosis and prognosis of such diseases. Using standard immunological techniques, the humoral immune system has been investigated by looking for circulating autoantibodies. Autoantibodies, like antinuclear, anti-dsDNA, and rheumatoid factor, have been identified for several diseases. These antibodies may not themselves be pathological, nor is the target they recognize in the body necessarily the same as that tested for in vitro; however, measurement of their levels aids in the diagnosis and in some cases has some prognostic and treatment implications.
Another methodology to study the adaptive immune system in autoimmune and lymphoid diseases is based on the analysis of the diversity of the adaptive immune cells. Activation of the adaptive immune cells leads to their clonal expansion. Evidence of this clonal expansion is usually obtained by amplification from the blood RNA or DNA of par of the nucleic acid sequence coding for the antigen recognition region. For example, PCR primers to amplify sequences that have a specific V segment of the β chain in T-cell receptor (analogous to antibody heavy chain) are used to amplify the J segments or J and D segments connected to the specific V segment. When a diverse cell population is present it is expected to amplify fragments with a distribution of slightly different size amplicons, but clonal expansion causes specific sizes to become enriched and thus more intense as visualized as bands on a gel. In the technique called “spectratyping” each of the V segments is amplified with the J and D segments to assess whether any of these amplicons shows a clonal expansion.
One problem of the spectratyping approach is that many distinct sequences can have the same length and hence are indistinguishable. Therefore only dramatic clonal expansion can be discerned by spectratyping. There is need to improve methods of diagnosing and aiding prognosis of autoimmune disease and autoimmune disease states as well as other diseases for which the immune system plays a central role.
While additional specificity in profiling the immune system would be of great utility in allowing its impact on human health to be better predicted, still greater utility would be delivered if methods were developed that would allow the specific T and B cells involved in disease processes to be identified even if those particular sequences had never before been observed. The vast diversity of the immune system provides it with an immense reserve of potentially useful cells but also presents a challenge to the researcher trying to use this repertoire for predictive purposes. Any single sequence targeting an antigen is one of a vast number that could be involved with and/or correlated to the disease process in a given individual. Methods that would identify which of the many cells in a given individual are involved with disease processes would be of great value to human health.
Immune cells profiling also has utility in the diagnosis and management of cancers. Treatment of cancers frequently involves the evaluation of response to treatment as well as monitoring for the recurrence of disease. Most common methodologies to monitor response and cancer recurrence are radiographic evaluations as well as blood biomarkers. For example, CT scans are frequently used to monitor cancer recurrence in multiple diseases including colon cancer. Similarly, protein biomarkers, like PSA and CEA, are blood biomarkers used to follow prostate and colon cancers. Specific genomic rearrangements generate another attractive target to use for following cancer cells. For example, the BCR-ABL translocation present in the vast majority or Chronic Myclogenous Leukemia (CML) patients has emerged as an analyte to assess the state of the disease. The specificity of the translocation to the leukemic cells and its amenability to be assayed by PCR technology allowed for the generation of a highly specific and sensitive test that is now used routinely to monitor CML patients.
Immune cell (or clonotype) profiling can be used to generate markers for lymphoid neoplasms. Cancer in the lymphoid cell lineage is a heterogeneous set of clinical diseases often reflecting the developmental stage of the cell that have undergone the transformation to a cancerous cell. Acute Lymphoblastic Leukemia (ALL) most often arises in immature lymphocytes. On the other hand, Multiple Myeloma (MM) occurs in plasma cells that have differentiated to produce antibodies. Similarly the different types of lymphomas often reflect different cell developmental stages. These diseases occur in different age groups, have different prognosis and mortality, and can be treated with distinct regimens.
These diseases are frequently treated with chemotherapy, radiotherapy, and/or bone marrow transplant. The disease recurrence is then monitored by different methods depending on the particular clinical situation. These methods include the assessment of blood and/or bone marrow using standard blood counts and morphology, flow cytometry (FCM) using cell surface markers, protein electrophoresis, as well as molecular techniques like PCR and FISH. In addition, radiographic studies like CT and PET scanning are frequently utilized for monitoring the recurrence of some of the lymphoid cancers. These methods suffer from invasiveness (bone marrow), cost and radiation risk, and/or lack of sensitivity.
Some molecular markers specific to a cancer cell detectable by PCR in a sensitive manner are present in a fraction of the lymphoid neoplasms. For example BCR-ABL is present in a fraction of ALL patients and it can serve as a marker to monitor for the relapse of the tumor. Unfortunately, for the majority of patients there are no such markers that can be used for sensitive and specific detection of relapse. FCM can be used to detect Minimum Residual Disease (MRD) which is useful for prognostic purposes. In this technique using multi-color Flow Activated Cell Sorting (FACS), a cancer cell can be identified by the virtue of the particular cell surface markers that it has. The sensitivity of this technique in the hands of experts is limited to <10−4, (1 cancer cell in 10,000 normal cells) and markers present at one time point may disappear later. Therefore FCM is generally not useful in detecting early relapse in blood samples.
PCR provides a sensitive methodology for detection of specific sequences and it has been used to detect the particular rearrangement in B cell receptor (BCRs) or T cell receptors (TCRs) of the cancer cell. This technique capitalizes on the fact that B or T cell receptors in a lymphocyte are created after imperfect recombination events that generate unique sequences for the different lymphocytes. For example, a TCR is comprised of TCRα and TCRβ chains. TCRα is created through the recombination that links one of several different V regions to one of several J regions. Similarly TCRβ is created through recombination that creates one V, D, and J segment in tandem. In both cases the recombination is often not perfect and some bases can be deleted from the germ line segment sequences and other bases (called the N and P bases) may be added. The sequence between the V and J segments is referred to as the NDN region.
These sequences can then serve as a tag for these lymphocytes and their progeny. Since these recombination events also occur in the cells that ultimately become malignant, unique sequences of the B and T cell receptors can serve as tags to detect the cancer cells. The tag sequence is patient specific, and in fact it may change in the same patient because of clonal evolution. To define the sequence of the T or B cell receptor from the leukemic cells for a patient the diagnostic leukemia sample that is usually highly enriched for the leukemic clone is used. For example, T and/or B cell receptor DNA is amplified from a diagnostic sample, and the product is run on a gel which can separate DNA based on size (sometime referred to as “spectratyping”); or alternatively heteroduplex analysis can be done. A large degree of skewing of the observed size distribution indicates monoclonal expansion, which may then be confirmed by sequencing a sample from the skewed separation peak. Without such subsequent sequencing, it is often difficult to determine whether such skewing has monoclonal or polyclonal origins, e.g. Van Dongen et al, U.S. patent publication 2006/0234234.
Once the sequence tag is identified, real time PCR using Taqman probes can be used to monitor the level of that sequence. The NDN region is usually not long enough to encompass the PCR primers and the detection oligonucleotide. Therefore typically PCR primers complementary to the V and J regions and a Taqman probe that include some of the NDN bases of the leukemic clone are used. The primers provide some of the specificity, as they amplify only a fraction of the entire repertoire. The specificity to the particular clonotype is provided by the hybridization of Taqman probe. Therefore the assay sensitivity is usually not as good as in a typical PCR (e.g., BCR-ABL) where the primer pair (with or without the Taqman probe) provides the specificity. It was shown that the sensitivity can be as high as 10−5 for some sequences but can be significantly worse depending on the hybridization specificity provided by the Taqman probe whose sequence is complementary to at least part of the NDN region. Given the low sensitivity for some probes the assay may not work for any of the rearrangements in a particular patient. The issue of clone evolution has also been raised previously further reducing the likelihood of detecting low level leukemia. In addition this technique is cumbersome requiring the generation of patient-specific Taqman probes as well as template to be used as standards. These patient-specific standards need to be used at each time the patient sample is to be tested. The inconsistency of the sensitivity among patients, the cumbersome nature, and the logistical issues of getting appropriate controls for the assay has greatly limited its use. Therefore there is a need to generate markers that can be used for relapse monitoring in patients with lymphoid neoplasms. In some embodiments the invention disclosed herein enables a very general, sensitive, and specific set of markers to be developed to manage patients with lymphoid cancers using immune cell sequencing.
It would be advantageous for many fields, including particularly the autoimmune and lymphoid cancer fields, if there were available assays for assessing clonotype profiles of individuals that were more sensitive and comprehensive than current techniques and that were generally applicable without the need of manufacturing individualized reagents.