Outputting cumulative sum for Cell array with strings and numbers

Cell1={
'A1'  5
'A2'  1
'A3'  2
'A4'  4
'A5'  1
'B1'  2
'B2'  6
'B3'  17
'B4'  8
'B5'  3
'C1'  7
'C2'  8
'D1'  1
.
.
.
};
I have a cell Cell1 which has varying row length. How can I say for example; for all As Bs Cs Ds Es etc .... count the values in column two. In the end, I would like to have an output like this 
'A'  13 
'B'  36 
'C'  15
'D'  1
etc...

Answer 1

[Andrei Bobrov]

Cell1={
'A1'  5
'A2'  1
'A3'  2
'A4'  4
'A5'  1
'B1'  2
'B2'  6
'B3'  17
'B4'  8
'B5'  3
'C1'  7
'C2'  8
'D1'  1};

S = regexp(Cell1(:,1),'^[A-Za-z]+','match');
S = [S{:}]';
[a,~,c] = unique(S);
out = [a num2cell(accumarray(c,cell2mat(Cell1(:,2))))];

[Eli Dim]

Thank you for your answer, it works perfectly.