Dendritic cells were first described in the late 19th century and are antigen-presenting cells of the immune system. There are multiple types of dendritic cells that originate from both lymphoid and myeloid lineages. Dendritic cells have several key functions, including activating T cells to launch immune responses, inducing tolerance to prevent autoimmunity, and stimulating B cell responses. They capture antigens and present them to T cells via MHC molecules to activate both CD4+ and CD8+ T cells. Dendritic cells play an important role in cancer immunotherapy by targeting tumor antigens to activate anti-tumor immune responses.

1. DENDRITIC CELLS
By
DR.BHAVIN VADODARIYA
DNB Surgical Oncology Resident,
Apollo CBCC Cancer Care,
Ahmedabad

2. HISTORY
 Dendritic cells were first described by Paul
Langerhans (hence "Langerhans cells") in the late
nineteenth century.
 The term "dendritic cells" was coined in 1973
by Ralph M. Steinman and Zanvil A. Cohn.
 For discovering the central role of dendritic cells in
the adaptive immune response, Steinman was
awarded the Nobel Prize in Physiology or
Medicine in 2011.

3.  Dendritic cells (DCs) are antigen-presenting
cells (also known as accessory cells) of the immune
system..
 At certain development stages they grow branched
projections, the dendrites that give the cell its name
déndron being Greek for "tree").

4. TYPES
 The most common division of dendritic cells is
"myeloid" and"plasmacytoid":
 Lymphoid and myeloid DCs evolve from lymphoid
and myeloid precursors, respectively, and thus are
of hematopoietic origin.

6. SUBSETS OF DCS.
 The two arms of the adaptive immune response —
humoral and cellular — are regulated by different
subsets of dendritic cells (DCs) in humans.
 Humoral immunity is preferentially regulated by
CD14+ dermal DCs, which produce interleukin-12
(IL-12). IL-12, in turn, acts directly on B cells and
promotes the development of T follicular helper
(TFH) cells.
 Cellular immune responses in the skin are
preferentially regulated by Langerhans cells.

7.  DCs can originate from both lymphoid and myeloid lineages.
In humans, myeloid lineage DCs are considered the
“classical” DC. These cells originate from myeloid commited
CD34+ progenitor cells, and monocytes can be driven to
become DCs in the presence of GM-CSF and TNFα ± IL-4.
 When this type of DC matures, it is known as an interstitial
DC. In addition to being able to activate naïve CD4 and CD8 T
cells, interstitial DCs can induce differentiation of naïve B cells
to antibody secreting plasma cells.
 Interstitial DCs are assumed to migrate to the lymphoid
follicles and become follicular DCs.

8. SUBTYPES OF DC

9.  Myeloid committed CD34+ cells which are CD14
negative can mature to what is called a Langerhans
DC, in the presence of TGF-β.
 Langerhans DC are also capable of activating naïve
T cells, but not B cells.
 Langerhans DC are those that capture antigen,
migrate to lymphoid tissues and present antigen to
T cells.

10.  The lymphoid DCs – the DC subset that originates
from CD34+ cells committed to the lymphoid
lineage, are CD11c- and are driven to become DCs
by IL-3.
 These DCs are referred to as Plasmacytoid DCs,
and they have the capacity to produce IFN-α and
reside in the T cell compartment of lymphoid
tissues.

11. Name Secretion Toll-like receptors
Conventional dendritic cell
(previously called Myeloid
dendritic cell) (cDC or
mDC)
Interleukin 12(IL-12) TLR 2, TLR 4
Plasmacytoid dendritic cell
(pDC)
Can produce high amounts
of interferon-alpha and
were previously
called interferon-producing
cells.[
TLR 7, TLR 9

12.  By contrast, follicular dendritic cells (FDC) are
probably of mesenchymal rather
than hematopoietic origin and do not express MHC
class II, but are so named because they are located
in lymphoid follicles and have long "dendritic"
processes.

13. IN BLOOD
Three types of DCs have been defined in blood:
 the CD1c+ myeloid DCs,-Chemokine production
 the CD141+ myeloid DCs –Cross Presentation
 CD303+ plasmacytoid DCs.- IFN-alpha Production

14. IN VITRO
 In some respects, dendritic cells cultured in vitro do
not show the same behaviour or capability as
dendritic cells isolated ex vivo. Nonetheless, they
are often used for research as they are still much
more readily available than genuine DCs.
 Mo-DC or MDDC refers to cells matured
from monocytes
 HP-DC refers to cells derived from hematopoietic
progenitor cells.

15.  It is also possible that Langerhans cells can
preferentially activate a dedicated subset of CD4+ T
cells that are specialized to help CD8+ cytotoxic T
lymphocytes (CTLs). Given their capacity to cross-
present antigens to CD8+ T cells, CD141+ DCs
might be involved in the development of CTL-
mediated responses.
 CD141+ DCs might also be involved in the
development of humoral responses through IL-12
secretion. PC, plasma cell.

16. LAUNCHING THE IMMUNE RESPONSE
 Antigens can reach lymph nodes through two pathways:
via lymphatics, where the antigen is captured by lymph
node-resident dendritic cells (DCs), or via tissue-
resident DCs.
 These immature DCs capture antigens, and DC
activation triggers their migration towards secondary
lymphoid organs and their maturation.

17.  Activated T cells drive DCs towards their terminal
maturation, which induces further expansion and
differentiation of T lymphocytes into effector T cells.
 If DCs do not receive maturation signals, they will
remain immature and antigen presentation will lead
to immune regulation and/or suppression. TReg
cell, regulatory T cell

19. FUNCTION OF DENDRITIC CELLS
T CELL ACTIVATION:
 DCs process and present antigen to activate both
CD4+ and CD8+ T cells. This appears to be the
most prominent role for DCs, since only DCs are
capable of activating naïve T cells.
 Immature DCs originate in the bone marrow and
migrate throughout the body. Once there, the
immature DCs lay dormant waiting to interact with
invading pathogens or other foreign bodies.

20.  At this point, the primary function of the immature
DC is to capture antigens.
 In the case of a wound accompanied by
inflammation, DCs are attracted to the area of
inflammation and stimulated to capture and
internally process antigens.
 So, the function of an immature DC is to find and
capture foreign bodies and antigens.
 Once captured, the antigen is processed either by
an exogenous or endosomal pathway, or by
endogenous or proteosomal pathway.

22.  For MHC class I presentation to stimulate CD8+
cytotoxic T cells, the antigen or protein is taken up
by phagocytosis or receptor mediated endocytosis
into the cytosol.
 The antigens are further degraded in the cytosol via
proteosome and enter the endoplasmic reticulum
where peptides bind to newly synthesized MHC
class I molecules for presentation on the cell
surface.

23.  Specific in vivo DC targeting with DC antibodies
fused with antigens and with DC activators is
shown.
 Targeting DCs in the tumour microenvironment to
reprogramme pro-tumour inflammation towards
tumour rejection is shown. MHC, major
histocompatibility complex; TLR, Toll-like receptor.


24.  For MHC class II presentation to stimulate CD4+ T
helper cells, antigen is taken up by phagocytosis or
receptor-mediated endocytosis to endosomes
where some proteolysis occurs.
 The peptides enter a vesicle containing MHC class
II where they bind and are transported to the cell
surface.

25. IMMUNE TOLERANCE:
 Central tolerance occurs in the thymus for T cells
and the bone marrow for B cells.
 The primary mechanism for central tolerance in T
cells is the induction of T cell death.
 DCs are found in abundance in the thymus, where
newly produced T cells are educated to become
functional CD4+ T cells and CD8+ T cells and
undergo selection to eliminate immunity against
‘self’.

26.  The mechanisms of peripheral tolerance include T
cell death, anergy, and active supression by T
regulatory cells.
 DCs could contribute by inducing apoptosis in T
cells and by producing IL-10, a cytokine that
stimulates T cells and induces T regulatory cells.
 DCs might also contribute to tolerance by inducing
anergy in responder T cells.

27. B CELL STIMULATION/FUNCTION:
 DCs can contribute to the stimulation of B cells,
both in the lymph node T cell areas and in germinal
centers.
 DCs produce a number of cytokines and factors
which are critical to the activation and differentiation
of B cells.

28.  The follicular DCs (FDCs), which are found in
germinal centers of lymph nodes, appear to be
important in the maintenance of B cell memory.
 FDCs are not involved in the initial antibody
response to foreign antigens. However, after the
initial antibody response begins, the FDCs form
numerous complexes of antigen and antibody.

29.  FDCs are believed to serve as both a ‘reservoir’ for
antibody and as a source of continued stimulation
for B cells.
 The B cells can in turn take up the antigen from
FDCs and present it to T cells.
 The reservoir of antigen and antibody complexes
on FDCs is believed to be able to last a very long
time, perhaps up to months or years.

30. DENDRITRIC CELL GENERATION:
 DCs can be generated by culturing CD34+ cells in
the presence of various cytokines.
 One approach which has been taken involves
depleting the CD34+ cells of differentiated
precursors and then culturing the cells in the
presence of GM-CSF and IL-4 ± TNF-α.
 CD34+ cells can be obtained from bone marrow,
cord blood or G-CSF mobilized peripheral blood.

32.  A key component on DCs in addition to antigen
capture, processing and presentation is the
presence of costimulatory molecules.
 DCs maintain on their cell surface costimulatory
molecules including members of the B7 family, TNF
family and intracellular adhesion molecules which
are critical to the activation of T cells and for the
proper homing of DCs before and after antigen
capture.

33.  Dendritic cell survives on an average of 3 weeks to
months, and during this period it is able to
selectively transform trillions of T cells.
 The robust anticancer immunology doesn’t allow
new malignant cells to grow and effectively stops or
delays tumor progression.
 Dendritic cells leading to IL-12 and TNF-alpha
generation also generate humoral immunology
which results in reducing cachexia.

34. DCS AND CANCER IMMUNOTHERAY
 Random targeting of dendritic cells (DCs) in
‘endogenous’ vaccination results from in vivo
antigen release owing to immunogenic cell death in
response to chemotherapy, radiotherapy and
immunomodulation approaches that are targeted at
T cells.
 Vaccines can be based on ex vivo-generated
tumour antigen-loaded DCs that are injected back
into patients.

36.  Another approach is to generate DC-like cells by
culturing CD14+ monocyte-enriched PBMC.
 In the presence of GM-CSF and IL-4, these cultures
give rise to large numbers of DC like cells.
 These monocyte-derived DCs need additional
conditioning in vitro with either TNF-α or monocyte-
conditioned media to be able to fully function as a DC
capable of priming antigen-specific T cell responses

37. DENDRITIC CELL IMMUNOTHERAPY
 DCs are being studied as adjuvants for vaccines or as a direct
therapy to induce immunity against cancer.
 DCs loaded with tumor lysates, tumor antigen-derived
peptides, MHC class I restricted peptides, or whole protein have
all been shown to generate anti-cancer immune responses and
activity, including in some cases the ability to induce complete
regression of existing tumor.
 Thus, there is a great desire to test these strategies and use
tumor-antigen bearing DCs as a vaccine in humans. Human
clinical trials are ongoing in several institutions to use DCs to
induce immunity to antigens against breast cancer, lung cancer,
melanoma, prostate and renal cell cancers.

38. S No. Trials Country Type of
Cancer
Phase No. of
Patients
1 BAYLOR
RESEARCH
INSTITUTE
USA Melanoma,
neoplasm
Metastasis
I & II 30
2 SAMSUNG
MEDICAL
CENTER
KOREA Prostatic
cancer
I & II 12
3 NATIONAL
CANCER
INSTITUTE
USA Melanoma I 20
4 HOAG
MEMORIAL
HOSPITAL
PRESBYTE
RIAN
Metastatic
Melanoma
I & II 80
5 HERLEV
HOSPITAL
DENMARK Advanced
Melanoma
I & II 25
6 STANFORD
UNIVERSIT
USA Multiple
Myloma
I & II 30

39. DENDRITIC CELL VACCINE
 Dendrtic cell Vaccine is an autologous (self) monocyte
derived Dendritic Cell immunotherapy which nurtures
the patient’s own mononuclear cells against cancer
specific cells
 Patients undergo apheresis for collection of blood
monocytes. These cells are cultured and processed for
the production of mature dendritic cells (DC) against the
specific tumor cell type, which are harvested on Day 8.
 Each dose of vaccine consists of dendritic cells (CD
80+, 83+, 86+,CD14-) more than 1 million in 15ml
 6 doses are given every 2 weeks for first 3 cycles and
next 3 cycles are given every 3 weeks.

40.  mature dendritic cells are infused to the same patient after eight
days of culture for generating specific anti-cancer immunity.
 After infusion, these dendritic cells along with specific cytokines
are carried to various lymph nodes and station themselves in
these lymph nodes.
 They start their physiological action on naïve T cells. Upon
physiological contact with dendrites of DC, T cells become
committed in the vicinity of dendritic cells. Each dendritic cell has
the potential to mature to about 3000-5000 T cells/hour.

43. SUMMARY
 DCs are being actively pursued as a means to
induce immunity in human patients.
 Since DCs are potent regulators of the immune
system, much research is being done to try to
understand how DCs can be harnessed to induce
immunity.

44.  While our understanding of DCs has evolved
tremendously in the 30 years since they were first
described, the use of DCs as a form of
immunotherapy is in it’s infancy.
 We are poised to learn whether and how DCs will
be useful as a tool in our arsenal to exploit human
immunity against disease